esnext's Introduction

esnext

Bring your JavaScript into the future.

Installation

$ npm install -g esnext

Usage

After installing, run esnext -h for comprehensive usage instructions.

Features

Functions

Translate some regular functions to arrow functions:

list.map(function(item) { return item.name; });

// ↑ becomes ↓

list.map(item => item.name);

Declarations

Convert var declarations to let or const as appropriate:

var arr = [];
for (var i = 0; i < 5; i++) {
  arr.push(i);
}

// ↑ becomes ↓

const arr = [];
for (let i = 0; i < 5; i++) {
  arr.push(i);
}

Objects

Use shorthand syntax for various object constructs:

let person = {
  first: first,
  last: last,
  
  fullName: function() {
    return `${first} ${last}`;
  }
};

// ↑ becomes ↓

let person = {
  first,
  last,
  
  fullName() {
    return `${first} ${last}`;
  }
};

Strings

Convert string concatenation to string or template literals:

let name = 'Brian' + ' ' + 'Donovan';
let greeting = 'Hello, ' + name;

// ↑ becomes ↓

let name = 'Brian Donovan';
let greeting = `Hello, ${name}`;

Destructuring

Convert assignments and declarations to use object destructuring syntax:

let a = obj.a, b = obj.b;
a = obj2.a, b = obj2.b;

// ↑ becomes ↓

let { a, b } = obj;
({ a, b } = obj2);

Modules

Translate CommonJS modules into ES6 modules:

var readFile = require('fs').readFile;
const MagicString = require('magic-string');
let { ok, strictEqual: eq } = require('assert');

exports.doSomething = function() {
  ok(1);
};

// ↑ becomes ↓

import { readFile } from 'fs';
import MagicString from 'magic-string';
import { ok, strictEqual as eq } from 'assert';

export function doSomething() {
  ok(1);
}

Options

{
  'declarations.block-scope': {
    /**
     * Set this to `true` to only turn `var` into `let`, never `const`.
     */
    disableConst: boolean
  }
}

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