changes a JavaScript anonymous function to an arrow function expression (ES 2015)
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README.md

vim-js-arrow-function

This plugin provides two functions related to JavaScript arrow functions.

The JsAnonFnToArrowFn function converts JavaScript anonymous functions to arrow function expressions (introduced in ES 2015).

It converts this:

function (p1, p2) {
  // some code
}

to this:

(p1, p2) => {
  // some code
}

and converts this:

function (n) { return n * 2; } 

to this:

n => n * 2

Place the cursor anywhere inside the function, even on the function keyword, and run the JsAnonFnToArrowFn command.

This command is mapped to <leader>af (for "arrow function") unless that is already mapped to something else.

The JsArrowFnBraceToggle function changes an arrow function from not using braces to using them and vice-versa. The cursor must be on a line that contains "=>".

It converts this:

const add = (p1, p2) => p1 + p2;

to this:

const add = (p1, p2) => { return p1 + p2; };

and converts in the opposite direction.

This command is mapped to <leader>tb (for "toggle braces") unless that is already mapped to something else.

The easiest way to install this is to use Pathogen and "git clone" this repository into the .vim/bundle directory.

Differences between arrow functions and the function keyword

This plug-in will perform a simple transformation from a function declared with the function keyword (a normal function) to an arrow function expression. There are differences between these that can affect the results.

When an arrow function has an expression body, the return keyword is implicit. However, when it has statement block, the return keyword is still required just like a normal function.

var example1 = function () { foo(); }; // example1() returns undefined

var example2 = () => { foo(); }; // example2() returns undefined

var example3 = () => foo(); // example3() returns the return value of foo()

Another difference is that normal functions always receive a this value, whereas arrow functions inherit the this value from its context.

$('a').each(function () { console.log(this); }; // logs all the "a" DOM elements

$('a').each(() => { console.log(this); }; // logs the window object

Resources: