In this article, an overview of MRI package is provided with a usage example picked from Changesets source code.
MRI package:
You can use MRI package to quickly scan for flags and arguments. It is an alternative to yargs-parser.
Install
npm install - save mri
Usage
// Example CLI with options
$ demo-cli - foo - bar=baz -mtv - hello world
The following code is picked from MRI npm package documentation.
const mri = require('mri');
const argv = process.argv.slice(2);
mri(argv);
//=> { _: ['hello', 'world'], foo:true, bar:'baz', m:true, t:true, v:true }
mri(argv, { boolean:['bar'] });
//=> { _: ['baz', 'hello', 'world'], foo:true, bar:true, m:true, t:true, v:true }
mri(argv, {
alias: {
b: 'bar',
foo: ['f', 'fuz']
}
});
//=> { _: ['hello', 'world'], foo:true, f:true, fuz:true, b:'baz', bar:'baz', m:true, t:true, v:true }
Read more about the options:
In essence, we get the CLI args converted into an object. Now that we understand the basics of MRI, it is time we look at its usage in Changesets.
MRI usage in Changesets:
MRI is found to be imported in Changesets CLI package
When you add a changeset using the command npx changeset add or npx changeset, these are accessed in the CLI package as shown below.
const args = process.argv.slice(2);
Parsing CLI args in changeset
The below code shows how mri used in Changeset CLI package
const parsed = mri(args, {
boolean: ["sinceMaster", "verbose", "empty", "open", "gitTag", "snapshot"],
string: [
"output",
"otp",
"since",
"ignore",
"tag",
"snapshot",
"snapshotPrereleaseTemplate",
],
alias: {
// Short flags
v: "verbose",
o: "output",
// Support kebab-case flags
"since-master": "sinceMaster",
"git-tag": "gitTag",
"snapshot-prerelease-template": "snapshotPrereleaseTemplate",
// Deprecated flags
"update-changelog": "updateChangelog",
"is-public": "isPublic",
"skip-c-i": "skipCI",
},
default: {
gitTag: true,
},
});
parsed value will look like below, I deduced this based on the documentation:
{
// string value (if you have used 'add' in npx changeset add)
['add'],
// boolean values
"sinceMaster": true,
"verbose": true,
"empty": true,
"open": true,
"gitTag": true,
"snapshot": true
// string values
// Note: if you have passed these options in your CLI, these keys will be parsed as string, no matter the what you pass in
// example: if you pass in - otp=123, 123 here, even though is a number, gets parsed as string since otp is configured to be parsed as
// string in the above code
"output",
"otp",
"since",
"ignore",
"tag",
"snapshot",
"snapshotPrereleaseTemplate",
// The alias option in mri allows you to define alternative names (aliases) for CLI arguments.
// This is particularly useful for supporting:
// Short flags: Such as -v for - verbose.
// Kebab-case flags: Allowing flags like - since-master to map to camelCase variables in JavaScript (e.g., sinceMaster).
// Deprecated flags: If you want to support older names for backward compatibility but still map them to the current property names.
}
parsed variable is used in a function named run imported from /run.ts
// run function call
run(parsed._, parsed, cwd).catch((err)
The first parameter is pared._ because in the documentation, it is provided that parsed commands like ‘add’ looks like { _: [‘add’]}
// run function definition
export async function run(
input: string[],
flags: { [name: string]: any },
cwd: string
) {
parsed contains mri parsed object based on the CLI args and the configuration set for booleans, strings, defaults, aliases.
cwd is a current working directory, you can get this with process.cwd()
About me:
Hey, my name is Ramu Narasinga. I study large open-source projects and create content about their codebase architecture and best practices, sharing it through articles, videos.
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