50+ hints JS(ES6+) developer must know (9th part)

Hi, everybody. Here is StormyTalent again!
And today we are going to see some more hints what JS developer must know.

1. Naming Conventions
Avoid single letter names. Be descriptive with your naming.

// bad
function q() {
  // ...
}

// good
function query() {
  // ...
}

Use camelCase when naming objects, functions, and instances.

// bad
const OBJEcttsssss = {};
const this_is_my_object = {};
function c() {}

// good
const thisIsMyObject = {};
function thisIsMyFunction() {}

Use PascalCase only when naming constructors or classes.

// bad
function user(options) {
  this.name = options.name;
}

const bad = new user({
  name: 'nope',
});

// good
class User {
  constructor(options) {
    this.name = options.name;
  }
}

const good = new User({
  name: 'yup',
});

Do not use trailing or leading underscores.

// bad
this.__firstName__ = 'Panda';
this.firstName_ = 'Panda';
this._firstName = 'Panda';

// good
this.firstName = 'Panda';

// good, in environments where WeakMaps are available
// see https://kangax.github.io/compat-table/es6/#test-WeakMap
const firstNames = new WeakMap();
firstNames.set(this, 'Panda');

Don’t save references to this. Use arrow functions or Function#bind.

// bad
function foo() {
  const self = this;
  return function () {
    console.log(self);
  };
}

// bad
function foo() {
  const that = this;
  return function () {
    console.log(that);
  };
}

// good
function foo() {
  return () => {
    console.log(this);
  };
}

A base filename should exactly match the name of its default export.

// file 1 contents
class CheckBox {
  // ...
}
export default CheckBox;

// file 2 contents
export default function fortyTwo() { return 42; }

// file 3 contents
export default function insideDirectory() {}

// in some other file
// bad
import CheckBox from './checkBox'; // PascalCase import/export, camelCase filename
import FortyTwo from './FortyTwo'; // PascalCase import/filename, camelCase export
import InsideDirectory from './InsideDirectory'; // PascalCase import/filename, camelCase export

// bad
import CheckBox from './check_box'; // PascalCase import/export, snake_case filename
import forty_two from './forty_two'; // snake_case import/filename, camelCase export
import inside_directory from './inside_directory'; // snake_case import, camelCase export
import index from './inside_directory/index'; // requiring the index file explicitly
import insideDirectory from './insideDirectory/index'; // requiring the index file explicitly

// good
import CheckBox from './CheckBox'; // PascalCase export/import/filename
import fortyTwo from './fortyTwo'; // camelCase export/import/filename
import insideDirectory from './insideDirectory'; // camelCase export/import/directory name/implicit "index"
// ^ supports both insideDirectory.js and insideDirectory/index.js

Use camelCase when you export-default a function. Your filename should be identical to your function’s name.

function makeStyleGuide() {
  // ...
}

export default makeStyleGuide;

Use PascalCase when you export a constructor / class / singleton / function library / bare object.

const AirbnbStyleGuide = {
  es6: {
  },
};

export default AirbnbStyleGuide;

Acronyms and initialisms should always be all uppercased, or all lowercased.

// bad
import SmsContainer from './containers/SmsContainer';

// bad
const HttpRequests = [
  // ...
];

// good
import SMSContainer from './containers/SMSContainer';

// good
const HTTPRequests = [
  // ...
];

// also good
const httpRequests = [
  // ...
];

// best
import TextMessageContainer from './containers/TextMessageContainer';

// best
const requests = [
  // ...
];

You may optionally uppercase a constant only if it (1) is exported, (2) is a const (it can not be reassigned), and (3) the programmer can trust it (and its nested properties) to never change.

// bad
const PRIVATE_VARIABLE = 'should not be unnecessarily uppercased within a file';

// bad
export const THING_TO_BE_CHANGED = 'should obviously not be uppercased';

// bad
export let REASSIGNABLE_VARIABLE = 'do not use let with uppercase variables';

// ---

// allowed but does not supply semantic value
export const apiKey = 'SOMEKEY';

// better in most cases
export const API_KEY = 'SOMEKEY';

// ---

// bad - unnecessarily uppercases key while adding no semantic value
export const MAPPING = {
  KEY: 'value'
};

// good
export const MAPPING = {
  key: 'value'
};

I would be happy if you read this material and gain a little bit inspirations.