What does => mean in node js

Question

I am learning node js, and came across '=>' several times, however struggle to understand what this means.

Here is an example:

app.post('/add-item', (req, res) => {
  // TODO: add an item to be posted
});

Do we actually need this in the above example? A simple explanation would be helpful. Thanks

score 41 · Accepted Answer · answered Sep 05 '16 at 10:10

41

It's nothing node-exclusive, it's an ES6 Arrow function expression

app.post('/add-item', (req, res) => {
  // TODO: add an item to be posted
});

basically means:

app.post('/add-item', function(req, res) {
  // TODO: add an item to be posted
});

The main difference between these two examples is that the first one lexically binds the this value.

answered Sep 05 '16 at 10:10

roberrrt-s

4

good answer, but I doubt `lexically binds the this value` means much to someone that thinks `=>` is exclusive to node.js – Christopher Reid Sep 05 '16 at 10:15
10

Yes @AllTheTime, but this could be usefull for anyone else that is looking for `=>` information. Therefor, I included it. – roberrrt-s Sep 05 '16 at 10:54
3

Nothing special about it. Lexical binding is a fancy word for static binding which in turn means that `this` doesn't change inside the anonymous function and always points to the object containing it. – Jun 16 '19 at 16:53

score 1 · Answer 2 · edited Sep 05 '16 at 11:44

1

This is just a different way of writing an anonymous function:

$(document).ready(() => {
    console.log('Hello I am typescript');
});

is equivalent to JavaScript:

$(document).ready(function(){
    console.log('Hello I am typescript');
});

edited Sep 05 '16 at 11:44

11684

answered Sep 05 '16 at 10:15

Vishal Gupta

it has two different, default return value on one-liners (no { }) and this is kept from the parent context (that's what you want for callbacks all the time most likely and better use regular functions otherwise) – localhostdotdev May 17 '19 at 00:02

2 Answers2