DeepSource for JavaScript/TypeScript Projects

DeepSource gives JavaScript and TypeScript projects a static analysis platform that goes well beyond what ESLint covers on its own. Its JavaScript analyzer detects over 100 issues across bug risks, security vulnerabilities, anti-patterns, and performance problems - with Autofix generating ready-to-apply code changes for many of those findings. For teams already running ESLint locally, DeepSource adds a CI/CD layer with a dashboard, PR comments, and automated remediation that turns code review into something closer to an automated workflow.

This guide covers everything needed to set up DeepSource for JavaScript and TypeScript projects - from the initial .deepsource.toml configuration to React, Next.js, and Node.js-specific rules, security issue detection, ESLint overlap, and test coverage integration with Jest and Vitest. For a broader overview of the platform, see our DeepSource review.

Why JavaScript teams use DeepSource

JavaScript's flexibility is both its greatest strength and its most consistent source of bugs. The language allows patterns that are syntactically valid but semantically wrong in ways that no linter configuration fully catches. Prototype pollution, unhandled promise rejections, incorrect hook dependency arrays, and XSS vectors from DOM string interpolation are all patterns that ship to production in well-maintained JavaScript codebases.

DeepSource's JavaScript analyzer is built specifically to catch these language-specific issues. Unlike ESLint, which relies on plugin ecosystems and requires careful configuration to cover React, Node.js, and TypeScript simultaneously, DeepSource's analyzer has built-in understanding of these environments. You declare which environment your project targets and DeepSource applies the relevant rule set automatically.

The other meaningful differentiator is Autofix. When DeepSource finds a var declaration that should be const, an unused import, or a missing await on an async call, it generates the corrected code as a diff. That diff is reviewable and one-click applicable from the PR comment thread. For routine code quality issues that would otherwise require developer time to fix, Autofix converts detection into automated remediation.

For JavaScript teams evaluating their options, the best code review tools for JavaScript guide covers the full landscape including DeepSource alongside competing platforms.

Setting up the JavaScript analyzer

The setup process for DeepSource on a JavaScript or TypeScript project requires two things: a .deepsource.toml configuration file and an activated repository in the DeepSource dashboard.

Step 1 - Create the .deepsource.toml file

The .deepsource.toml file belongs in the root of your repository. For a JavaScript project, the minimum configuration is:

version = 1

[[analyzers]]
name = "javascript"
enabled = true

This enables the JavaScript analyzer with default settings. DeepSource analyzes all .js, .jsx, .ts, and .tsx files in the repository.

Step 2 - Configure the environment

The analyzers.meta section tells DeepSource which JavaScript environment your project targets. This determines which rule sets apply:

version = 1

[[analyzers]]
name = "javascript"
enabled = true

  [analyzers.meta]
  environment = ["nodejs"]

The environment field accepts an array of values. The available environments are:

• "browser" - Client-side JavaScript with DOM APIs
• "nodejs" - Node.js server-side code
• "react" - React component code (includes browser APIs)
• "nextjs" - Next.js projects (includes React and Node.js rules)
• "jest" - Jest test environment globals

You can combine environments for projects that span multiple contexts:

[analyzers.meta]
environment = ["browser", "react", "jest"]

This is the right configuration for a Create React App or Vite project with Jest tests. The jest environment prevents DeepSource from flagging Jest globals like describe, it, expect, and beforeEach as undefined variables.

Step 3 - Add test file patterns

If your test files live outside standard locations like __tests__ or alongside source files with .test.ts or .spec.ts suffixes, configure the test_patterns setting so DeepSource applies test-appropriate rules:

[analyzers.meta]
environment = ["nodejs", "react"]
test_patterns = ["**/*.test.{js,ts,jsx,tsx}", "**/*.spec.{js,ts,jsx,tsx}", "tests/**"]

Without test_patterns, DeepSource may apply production code rules to test files and flag patterns like jest.mock() or vi.mock() that are only valid in test contexts.

Step 4 - Add a transformer for formatting

DeepSource transformers run code formatters automatically on every commit. For JavaScript and TypeScript projects, the Prettier transformer handles formatting without any additional configuration:

version = 1

[[analyzers]]
name = "javascript"
enabled = true

  [analyzers.meta]
  environment = ["nodejs", "react"]

[[transformers]]
name = "prettier"
enabled = true

You can also add the ESLint transformer to run ESLint auto-fixes through DeepSource:

[[transformers]]
name = "eslint"
enabled = true

Step 5 - Activate the repository

After pushing the .deepsource.toml file to your default branch, go to the DeepSource dashboard and activate your repository. The first analysis runs immediately. For a typical JavaScript or TypeScript project (20,000-100,000 lines), the initial analysis completes in 3-8 minutes.

For more detail on the .deepsource.toml configuration format and all available settings, see our guide on DeepSource TOML configuration.

TypeScript-specific configuration

DeepSource handles TypeScript through the same JavaScript analyzer. No separate analyzer block is needed. However, there are TypeScript-specific settings and rules worth understanding.

Full TypeScript project setup

For a TypeScript project targeting Node.js or React, the configuration looks like:

version = 1

[[analyzers]]
name = "javascript"
enabled = true

  [analyzers.meta]
  environment = ["nodejs"]

DeepSource automatically detects .ts and .tsx files and applies TypeScript-aware analysis. It uses your tsconfig.json to understand the project structure, resolve module paths, and determine which TypeScript compiler options are in effect.

TypeScript-specific rules

DeepSource's JavaScript analyzer includes rules that only apply to TypeScript code:

Incorrect type assertions:

// DeepSource flags this - using 'as any' defeats type safety
function processUser(data: unknown) {
  const user = data as any;
  return user.name.toUpperCase();
}

// Better: use type guard or proper assertion
function processUser(data: unknown) {
  if (typeof data === 'object' && data !== null && 'name' in data) {
    return (data as { name: string }).name.toUpperCase();
  }
  throw new Error('Invalid user data');
}

Non-null assertion misuse:

// DeepSource flags excessive non-null assertions
function getLength(str: string | null) {
  return str!.length; // Dangerous: throws if str is null
}

// Correct: handle null explicitly
function getLength(str: string | null) {
  if (str === null) return 0;
  return str.length;
}

Missing return type annotations:

DeepSource can flag exported functions missing explicit return type annotations, which is useful for enforcing type documentation on public APIs. This rule is configurable and many teams disable it for internal utility functions while keeping it enabled for exported module interfaces.

React and Next.js patterns

React projects have their own category of issues that general JavaScript rules do not cover. DeepSource's react environment activates a dedicated set of React-specific rules.

React hooks rules

The hooks rules are among the most valuable for React projects. Incorrect hook usage causes subtle bugs that can be difficult to trace back to their source:

Missing hook dependencies:

// DeepSource flags missing dependencies in useEffect
function UserProfile({ userId }: { userId: string }) {
  const [user, setUser] = useState(null);

  useEffect(() => {
    fetchUser(userId).then(setUser);
    // DeepSource: userId is used inside but not in dependency array
  }, []); // Should be [userId]

  return <div>{user?.name}</div>;
}

Conditional hook calls:

// DeepSource flags hooks called conditionally
function ConditionalComponent({ isLoggedIn }: { isLoggedIn: boolean }) {
  if (!isLoggedIn) {
    return ;
  }

  // DeepSource: hooks must not be called after conditional return
  const [data, setData] = useState(null);
  useEffect(() => { fetchData().then(setData); }, []);

  return ;
}

Object literals in JSX props:

// DeepSource flags inline object creation in JSX props
function UserList({ users }: { users: User[] }) {
  return (

  );
}

// Better: define outside component or use useMemo
const COLUMNS = [{ key: 'name', label: 'Name' }];
const TABLE_STYLE = { marginTop: 16 };

function UserList({ users }: { users: User[] }) {
  return ;
}

Inline object and array literals in JSX props cause unnecessary re-renders because React sees a new reference on every render cycle. This is a common React performance anti-pattern that DeepSource catches automatically.

Next.js-specific rules

When you set environment = ["nextjs"], DeepSource applies additional rules for Next.js patterns:

getServerSideProps and getStaticProps:

// DeepSource flags missing return type in data fetching functions
export async function getServerSideProps(context) {
  const data = await fetchData(context.params.id);
  // DeepSource: should return { props: { data } }
  return data; // Incorrect - returns data directly
}

// Correct pattern
export async function getServerSideProps(context: GetServerSidePropsContext) {
  const data = await fetchData(context.params!.id as string);
  return { props: { data } };
}

Next.js Image component:

// DeepSource flags missing width/height on Next.js Image
function Banner() {
  return (

  );
}

API route error handling:

// pages/api/users.ts

// DeepSource flags missing error handling in API routes
export default async function handler(req: NextApiRequest, res: NextApiResponse) {
  const users = await db.query('SELECT * FROM users');
  // DeepSource: no try/catch - unhandled promise rejection crashes server
  res.status(200).json(users);
}

// Correct pattern
export default async function handler(req: NextApiRequest, res: NextApiResponse) {
  try {
    const users = await db.query('SELECT * FROM users');
    res.status(200).json(users);
  } catch (error) {
    res.status(500).json({ error: 'Internal server error' });
  }
}

Node.js patterns

For server-side JavaScript with environment = ["nodejs"], DeepSource applies rules specific to the Node.js runtime and its common patterns.

Unhandled promise rejections:

// DeepSource flags missing catch on promises
app.get('/users', (req, res) => {
  db.findAll()  // Promise with no .catch() or await/try-catch
    .then(users => res.json(users));
});

// Correct with async/await
app.get('/users', async (req, res) => {
  try {
    const users = await db.findAll();
    res.json(users);
  } catch (error) {
    res.status(500).json({ error: error.message });
  }
});

Synchronous I/O in request handlers:

const fs = require('fs');

// DeepSource flags synchronous fs methods in Express handlers
app.get('/config', (req, res) => {
  const config = fs.readFileSync('./config.json', 'utf8'); // Blocks event loop
  res.json(JSON.parse(config));
});

// Correct: use async version
app.get('/config', async (req, res) => {
  const config = await fs.promises.readFile('./config.json', 'utf8');
  res.json(JSON.parse(config));
});

Missing input validation in Express routes:

// DeepSource flags direct use of req.query/req.body without validation
app.post('/api/users', (req, res) => {
  const { email, role } = req.body;
  // No validation - attacker can set role to 'admin'
  db.createUser({ email, role });
  res.status(201).json({ success: true });
});

ESLint overlap and how to think about it

One of the most common questions about DeepSource for JavaScript teams is whether it conflicts with or duplicates an existing ESLint setup. The honest answer is: there is some overlap, but the tools serve different roles in the development workflow.

Where ESLint is stronger

ESLint runs in milliseconds via pre-commit hooks and provides instant feedback as developers type. Its plugin ecosystem is unmatched - eslint-plugin-react, @typescript-eslint/eslint-plugin, eslint-plugin-security, and hundreds of others give ESLint coverage that no single alternative matches. If you have a well-configured ESLint setup with appropriate plugins, you are already catching many of the issues that DeepSource detects.

ESLint also allows highly granular rule configuration. You can enable or disable specific rules, set severity levels, use inline disable comments, and configure rules per-directory using .eslintrc overrides.

Where DeepSource adds value on top of ESLint

DeepSource operates in CI/CD rather than locally. Its value add over ESLint is in four areas:

Dashboard and trend tracking - ESLint has no concept of code health over time. DeepSource tracks issues by category, severity, and file over every commit, giving you visibility into whether the codebase is improving or accumulating debt.

PR integration - DeepSource posts comments on pull requests with specific findings, linking to the dashboard for more context. This surfaces issues during code review without requiring reviewers to run ESLint locally.

Autofix at scale - While ESLint has --fix, it requires developers to run it locally and commit the changes. DeepSource Autofix generates fixes that appear as reviewable diffs in the PR, can be applied with one click, and are committed by the DeepSource bot. This is particularly useful for large codebases with many existing issues.

Security analysis - DeepSource's security rules go deeper than most ESLint security plugins. The eslint-plugin-security rules are a good start but they cover a fraction of what DeepSource detects, particularly for XSS and prototype pollution vectors.

The practical recommendation is to keep ESLint running locally for fast feedback and configure DeepSource in CI/CD for dashboard tracking, PR integration, and automated fixes.

Security issues DeepSource detects in JavaScript

Security analysis is where DeepSource adds the most unique value for JavaScript projects, particularly for browser code and Node.js APIs.

XSS vulnerabilities

Cross-site scripting is the most prevalent JavaScript security issue and DeepSource catches several XSS patterns:

// DOM-based XSS via innerHTML
function renderMessage(userInput: string) {
  document.getElementById('message')!.innerHTML = userInput;
  // DeepSource: XSS via unescaped innerHTML assignment
}

// XSS via document.write
function insertContent(url: string) {
  document.write('<script src="' + url + '"></script>');
  // DeepSource: XSS via document.write with user-controlled input
}

// React: dangerouslySetInnerHTML without sanitization
function Comment({ content }: { content: string }) {
  return (
    <div dangerouslySetInnerHTML={{ __html: content }} />
    // DeepSource: potential XSS - content should be sanitized before dangerouslySetInnerHTML
  );
}

For React projects, DeepSource specifically flags dangerouslySetInnerHTML usage where the value originates from user input or external data sources without explicit sanitization.

Prototype pollution

Prototype pollution is a JavaScript-specific vulnerability class that allows attackers to modify Object.prototype and affect all objects in the application:

// DeepSource flags unsafe recursive object merge
function merge(target, source) {
  for (const key in source) {
    // No hasOwnProperty check - allows __proto__ pollution
    if (typeof source[key] === 'object') {
      target[key] = merge(target[key] || {}, source[key]);
    } else {
      target[key] = source[key];
    }
  }
  return target;
}

// Correct: check hasOwnProperty and block __proto__
function safeMerge(target, source) {
  for (const key of Object.keys(source)) {
    if (key === '__proto__' || key === 'constructor') continue;
    if (typeof source[key] === 'object' && source[key] !== null) {
      target[key] = safeMerge(target[key] || {}, source[key]);
    } else {
      target[key] = source[key];
    }
  }
  return target;
}

Prototype pollution vulnerabilities have been found in popular npm packages including lodash, jQuery, and node-fetch. DeepSource detects the patterns that create these vulnerabilities in your own code.

Command injection in Node.js

const { exec } = require('child_process');

// DeepSource flags exec with user-controlled input
app.post('/convert', (req, res) => {
  const filename = req.body.filename;
  // Command injection: attacker can set filename to "file.pdf; rm -rf /"
  exec(`convert ${filename} output.png`, (error, stdout) => {
    res.json({ output: stdout });
  });
});

// Correct: use execFile with argument array instead of exec
const { execFile } = require('child_process');

app.post('/convert', (req, res) => {
  const filename = path.basename(req.body.filename); // Sanitize first
  execFile('convert', [filename, 'output.png'], (error, stdout) => {
    res.json({ output: stdout });
  });
});

eval() and Function constructor misuse

// DeepSource flags eval() with dynamic input
function processExpression(userInput: string) {
  return eval(userInput); // Arbitrary code execution
}

// DeepSource flags Function constructor with dynamic content
const fn = new Function('x', userExpression); // Code injection

// DeepSource flags setTimeout/setInterval with string argument
setTimeout("doSomething()", 1000); // eval-equivalent

Hardcoded secrets

// DeepSource detects credential patterns in JavaScript files
const API_KEY = "sk-proj-abc123xyz789";
const DB_PASSWORD = "production_password_2026";
const AWS_SECRET = "wJalrXUtnFEMI/K7MDENG/bPxRfiCYEXAMPLEKEY";

// These patterns trigger DeepSource security findings regardless of context

For a broader comparison of how DeepSource handles security scanning versus dedicated tools, see our Semgrep overview and the Codacy platform comparison.

Autofix for JavaScript and TypeScript

DeepSource Autofix generates concrete code changes for JavaScript and TypeScript issues. For JS/TS projects, the fixes cover a wide range of routine code quality issues.

Common JavaScript autofixes

var to const/let conversion:

// Before (DeepSource detects var usage)
var userName = getUserName();
var items = [];
var MAX_COUNT = 100;

// After (Autofix-generated)
const userName = getUserName();
const items = [];
const MAX_COUNT = 100;

Unused variable and import removal:

// Before

function SimpleComponent() {
  const [data, setData] = useState(null);
  // useCallback and axios are never used

  useEffect(() => {
    fetch('/api/data').then(r => r.json()).then(setData);
  }, []);

  return <div>{data}</div>;
}

// After (Autofix removes unused imports)

function SimpleComponent() {
  const [data, setData] = useState(null);

  useEffect(() => {
    fetch('/api/data').then(r => r.json()).then(setData);
  }, []);

  return <div>{data}</div>;
}

Missing await on async function calls:

// Before (DeepSource detects missing await)
async function saveUser(user: User) {
  db.save(user); // Returns a Promise but result is ignored
  return { success: true };
}

// After (Autofix adds await)
async function saveUser(user: User) {
  await db.save(user);
  return { success: true };
}

Promise chain to async/await conversion:

For complex promise chains, DeepSource can suggest converting to async/await syntax, which is more readable and less error-prone:

// Before
function loadUserData(userId) {
  return fetchUser(userId)
    .then(user => fetchPermissions(user.id))
    .then(permissions => fetchSettings(permissions.settingsId))
    .then(settings => ({ settings }))
    .catch(err => ({ error: err.message }));
}

// After (Autofix-generated async/await equivalent)
async function loadUserData(userId) {
  try {
    const user = await fetchUser(userId);
    const permissions = await fetchPermissions(user.id);
    const settings = await fetchSettings(permissions.settingsId);
    return { settings };
  } catch (err) {
    return { error: err.message };
  }
}

Autofix confidence levels

Not all JavaScript fixes are equally safe to apply without review. DeepSource categorizes fixes by confidence:

• High confidence - Mechanical transformations like unused import removal, var to const, missing semicolons. Safe to apply without review.
• Medium confidence - Hook dependency arrays, promise handling patterns. Review the diff to ensure the fix matches the intended behavior.
• Low confidence - Logic-affecting changes like security fixes. Always review before applying.

The dashboard surfaces confidence level for each fix, allowing teams to auto-approve high-confidence fixes while routing others through code review.

Test coverage with Jest and Vitest

DeepSource integrates with JavaScript test runners through its coverage data ingestion pipeline. The process works the same way regardless of whether you use Jest, Vitest, Mocha, or another runner that outputs LCOV coverage data.

Jest coverage setup

Generate an LCOV coverage report from Jest:

# Run Jest with coverage in LCOV format
npx jest --coverage --coverageReporters=lcov

# Coverage report is generated at ./coverage/lcov.info

Then upload it to DeepSource using the CLI:

# Install the DeepSource CLI
curl https://deepsource.io/cli | sh

# Upload coverage data
DEEPSOURCE_DSN=https://[e-mail] \
  ./bin/deepsource report \
    --analyzer javascript \
    --key javascript \
    --value-file coverage/lcov.info

Vitest coverage setup

Vitest uses the same LCOV format. Configure it in vite.config.ts:

// vite.config.ts

export default defineConfig({
  test: {
    coverage: {
      provider: 'v8',
      reporter: ['lcov', 'text'],
      reportsDirectory: './coverage',
    },
  },
});

Then run and upload:

npx vitest run --coverage

DEEPSOURCE_DSN=https://[e-mail] \
  ./bin/deepsource report \
    --analyzer javascript \
    --key javascript \
    --value-file coverage/lcov.info

GitHub Actions integration

A complete GitHub Actions workflow that runs tests and uploads coverage to DeepSource:

# .github/workflows/test.yml
name: Test and Coverage
on: [push, pull_request]

jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4

      - uses: actions/setup-node@v4
        with:
          node-version: '20'
          cache: 'npm'

      - run: npm ci

      - name: Run tests with coverage
        run: npm test -- --coverage --coverageReporters=lcov

      - name: Upload coverage to DeepSource
        run: |
          curl https://deepsource.io/cli | sh
          ./bin/deepsource report \
            --analyzer javascript \
            --key javascript \
            --value-file coverage/lcov.info
        env:
          DEEPSOURCE_DSN: ${{ secrets.DEEPSOURCE_DSN }}

Once coverage data flows into DeepSource, the dashboard shows coverage percentage per file and per function, tracks coverage trends across commits, and flags files where coverage has dropped below configured thresholds.

Advanced .deepsource.toml configuration for JavaScript projects

Excluding generated and vendor files

JavaScript projects often contain generated files - bundler output, TypeScript declaration files, third-party vendor code - that should not be analyzed:

version = 1

exclude_patterns = [
  "dist/**",
  "build/**",
  ".next/**",
  "node_modules/**",
  "coverage/**",
  "**/*.min.js",
  "**/*.bundle.js",
  "public/static/**",
  "src/generated/**",
]

[[analyzers]]
name = "javascript"
enabled = true

  [analyzers.meta]
  environment = ["react", "nodejs"]

Monorepo configuration

For monorepos with multiple JavaScript packages:

version = 1

exclude_patterns = [
  "**/node_modules/**",
  "**/dist/**",
  "**/build/**",
]

[[analyzers]]
name = "javascript"
enabled = true

  [analyzers.meta]
  environment = ["react", "nodejs", "jest"]
  test_patterns = [
    "**/*.test.{js,ts,jsx,tsx}",
    "**/*.spec.{js,ts,jsx,tsx}",
    "**/__tests__/**",
  ]

[[transformers]]
name = "prettier"
enabled = true

DeepSource analyzes all JavaScript and TypeScript files across packages in the monorepo unless explicitly excluded. The Team plan includes monorepo support without additional configuration.

DeepSource compared to alternatives for JavaScript

DeepSource vs. Codacy

Codacy aggregates multiple JavaScript analysis tools including ESLint, TSLint, and others into a unified dashboard. It supports 40+ languages and costs $15/user/month. DeepSource runs its own proprietary analyzer at $24/user/month with a lower false positive rate and Autofix that Codacy does not offer. For JavaScript-focused teams where Autofix provides tangible time savings, DeepSource's higher per-seat cost is often justified. For polyglot teams needing broad language coverage with a lighter budget, Codacy is the more practical choice.

DeepSource vs. Semgrep

Semgrep is a pattern-matching static analysis engine with a large community ruleset for JavaScript security. It is highly customizable - security teams can write their own Semgrep rules in YAML to codify organization-specific patterns. DeepSource is simpler to configure and adds the dashboard, PR integration, and Autofix that Semgrep does not provide out of the box. For teams that want to write custom security rules, Semgrep is the stronger choice. For teams that want a fully managed platform with minimal configuration, DeepSource is more appropriate.

CodeAnt AI as a modern alternative

CodeAnt AI is a modern code quality platform priced at $24-40/user/month that offers AI-powered analysis for JavaScript and TypeScript projects. Unlike DeepSource's primarily rule-based approach, CodeAnt AI uses AI models to detect code quality issues, security vulnerabilities, and anti-patterns - including context-dependent problems that deterministic rules miss.

For JavaScript teams where the quality of AI-driven suggestions outweighs the predictability of rule-based analysis, CodeAnt AI is worth evaluating alongside DeepSource. The two tools have similar pricing tiers, making a side-by-side trial on a real codebase the most practical way to compare them.

For a comprehensive comparison of all DeepSource alternatives, see the DeepSource alternatives guide.

Getting started with DeepSource for JavaScript

Here is a practical setup checklist for JavaScript and TypeScript projects:

1. Create a .deepsource.toml file in the repository root
2. Set the JavaScript analyzer enabled = true and configure the correct environment values for your project
3. Add test_patterns if your test files use non-standard naming or locations
4. Add the Prettier transformer if you want automated formatting
5. Configure exclude_patterns for dist/, build/, node_modules/, and any generated files
6. Push the config to your default branch and activate the repository in the DeepSource dashboard
7. Review the initial analysis baseline and suppress any false positives
8. Set up coverage reporting in your Jest or Vitest CI workflow
9. Add DEEPSOURCE_DSN as a secret in your CI environment

After the initial setup, DeepSource runs on every push and pull request. The tool page at /tool/deepsource covers pricing, plan comparison, and the full feature set.

For JavaScript teams coming from Python projects already using DeepSource, the DeepSource for Python guide covers the differences in analyzer configuration between the two languages. The .deepsource.toml structure is identical - only the name and meta fields change between analyzers.

The combination of a shallow ESLint setup running locally with DeepSource handling CI/CD analysis, PR integration, and automated fixes represents the most efficient JavaScript static analysis workflow for most teams in 2026. The tools complement each other rather than compete, and the full stack requires less configuration overhead than trying to match DeepSource's feature set with open-source tools alone.

Further Reading

• Unit Testing with Mocha and Chai: The Complete JavaScript Guide
• dangerouslySetInnerHTML in React: Complete Guide to Safe HTML Rendering
• AI Code Review for Enterprise Teams: Security, Compliance, and Scale in 2026
• Will AI Replace Code Reviewers? What the Data Actually Shows
• The State of AI Code Review in 2026 - Trends, Tools, and What's Next
• How to Set Up AI Code Review in GitHub Actions - Complete Guide
• Best AI Code Review Tools in 2026 - Expert Picks

Frequently Asked Questions

How do I set up DeepSource for a JavaScript project?

Create a .deepsource.toml file in the root of your repository with the JavaScript analyzer enabled. Set the environment under analyzers.meta to javascript, nodejs, or browser depending on your project. Push the config file to your default branch and activate the repository in the DeepSource dashboard at app.deepsource.com. DeepSource will run its first analysis automatically on all .js and .jsx files.

Does DeepSource support TypeScript?

Yes. DeepSource's JavaScript analyzer fully supports TypeScript. It analyzes .ts and .tsx files using the same analyzer block as JavaScript - you do not need a separate configuration for TypeScript. Set the environment to nodejs or react depending on your project type. DeepSource detects TypeScript-specific issues like incorrect type assertions, missing null checks on potentially undefined values, and misuse of the any type.

How do I configure DeepSource for a React project?

In your .deepsource.toml file, add a JavaScript analyzer block and set the environment to react under analyzers.meta. DeepSource will apply its React-specific rules covering hooks usage (dependency arrays, conditional hooks), prop types, component patterns, and performance anti-patterns like object literals in JSX props. If you are using Next.js, set the environment to nextjs and DeepSource also applies Next.js-specific rules.

Does DeepSource overlap with ESLint?

There is some overlap between DeepSource and ESLint, but they serve different roles. ESLint runs locally and in pre-commit hooks with extensive plugin ecosystems for React, TypeScript, and Node.js. DeepSource runs in CI/CD with a dashboard, PR integration, and Autofix. DeepSource does not replace ESLint - it adds a layer of deeper analysis, security scanning, and automated fixes on top of your existing ESLint setup. Many teams run both without conflict.

What security issues does DeepSource detect in JavaScript?

DeepSource's JavaScript analyzer detects XSS vulnerabilities from unescaped user input in DOM manipulation and dangerouslySetInnerHTML, prototype pollution through object extension without hasOwnProperty checks, command injection in Node.js via exec and spawn with user-controlled input, SQL injection in database query strings, hardcoded secrets and API keys, insecure use of eval(), and prototype chain manipulation. Security findings include the relevant CWE identifier for compliance documentation.

How does DeepSource Autofix work for JavaScript and TypeScript?

When DeepSource detects a JavaScript or TypeScript issue with an available fix, it generates a concrete code diff that resolves the problem. For JS/TS, Autofix handles issues like removing unused variables and imports, converting var declarations to let or const, replacing deprecated API calls, fixing missing await on async functions, correcting React hook dependency arrays, and applying modern JavaScript idioms. You can apply fixes individually from the dashboard or in bulk directly from PR comments.

Does DeepSource work with Jest and Vitest for coverage?

Yes. DeepSource accepts coverage data from Jest, Vitest, and other coverage tools that output data in LCOV or XML format. You generate a coverage report with your test runner, then upload it to DeepSource using the deepsource CLI with the javascript analyzer key. DeepSource tracks coverage trends over time and can flag files or functions with insufficient coverage directly in the dashboard.

Can DeepSource analyze Node.js backend code?

Yes. Set the environment to nodejs in your .deepsource.toml analyzer configuration and DeepSource applies Node.js-specific rules alongside its general JavaScript rules. These cover patterns like uncaught promise rejections, synchronous I/O calls in hot paths, missing error handling in callbacks, insecure child_process usage, path traversal vulnerabilities in file system operations, and missing input validation in Express route handlers.

What is the .deepsource.toml config for TypeScript with React?

For a TypeScript React project, your .deepsource.toml should have a JavaScript analyzer block with enabled set to true and environment set to react under analyzers.meta. If you also use a test framework, add the test_patterns setting. You can add a prettier or eslint transformer block for automated formatting. The version field at the top of the file should be set to 1.

How does DeepSource compare to Semgrep for JavaScript security?

DeepSource and Semgrep take different approaches to JavaScript security analysis. Semgrep is a pattern-matching engine where you write or import rules as code patterns - it has extensive community rulesets for JavaScript security including OWASP Top 10 patterns. DeepSource uses a proprietary analyzer with built-in rules and adds a SaaS platform with PR integration and Autofix. Semgrep is more customizable for security teams that want to write their own rules. DeepSource is simpler to set up and provides broader code quality coverage beyond security.

Does DeepSource support Next.js?

Yes. DeepSource includes Next.js-specific analysis when you set the environment to nextjs in your .deepsource.toml configuration. It detects patterns like improper use of getServerSideProps and getStaticProps, missing key props in list rendering, incorrect Image component usage, and anti-patterns in API route handlers. Next.js rules apply on top of the standard JavaScript and React rule sets.

How much does DeepSource cost for JavaScript teams?

DeepSource pricing is not language-specific. The Open Source plan is free for public repositories. The Team plan costs $24/user/month with annual billing and includes unlimited Autofix, private repository support, monorepo analysis, and bundled AI Review credits. Enterprise pricing is custom. DeepSource counts active committers for billing - team members who only review dashboards without pushing code are not charged.

---

Originally published at aicodereview.cc