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functiontypestypescript
Jean-Philippe Pellet
Jean-Philippe Pellet

Reputation: 59994

TypeScript: difference between function types

What's the formal difference between the types of these two variables in TypeScript?

var randomStringId = () => Math.random().toString(36).substr(2, 9);
function randomStringId2() {
    return Math.random().toString(36).substr(2, 9);
}

randomStringId has type () => string. randomStringId2 has type (): string. Are they different? If yes, how? Or is it just my IDE showing differently two types that are fundamentally the same?

Upvotes: 0

Views: 931

Answers (2)

basarat
basarat

Reputation: 276309

Absolutely no difference in the Types. Both are exactly the same. They take nothing and return a string.

Here is the proof : 

interface Foo1{
    foo:()=>string;
}
interface Foo2{
    foo():string;
}
var foo1:Foo1;
var foo2:Foo2;
foo1 = foo2 = foo1;

However there is a difference in the way they behave. To understand the need for a lambda function ()=> : http://youtube.com/watch?v=tvocUcbCupA&hd=1

Upvotes: 1

Alexey Vagarenko
Alexey Vagarenko

Reputation: 1196

Your functions are the same. However, these two functions are not:

var getX = () => this.x

function getX() {
    return this.x
}

look at the generated js code:

var _this = this;
var getX = function () {
    return _this.x;
};

function getX() {
   return this.x;
}

The function defined with arrow notation () => captures the reference to this when it is defined.

Upvotes: 3

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