TypeScript: difference between function types

Question

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?

To understand the lambda syntax : youtube.com/watch?v=tvocUcbCupA&hd=1 — basarat
– basarat, Commented May 7, 2014 at 10:33
You have to be careful as the first one is a variable holding a function, and the second one is a defined function itself. randomStringId2 can be used BEFORE its declaration, while randomStringId cannot. This is pure JavaScript differences and since TypeScript is a superset of JavaScript, it inherits this difference. — Stephen Chung
– Stephen Chung, Commented May 8, 2014 at 5:21

Alexey Vagarenko · Accepted Answer · 2014-05-07 10:31:49Z

3

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.

answered May 7, 2014 at 10:31

Alexey Vagarenko

1,2068 silver badges15 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

basarat · Accepted Answer · 2014-05-07 10:35:32Z

1

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

edited May 7, 2014 at 10:35

answered May 7, 2014 at 10:29

basarat

278k60 gold badges475 silver badges528 bronze badges

Collectives™ on Stack Overflow

TypeScript: difference between function types

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related