What does the symbol ":" mean in Javascript?

Question

I found this code in Ionic framework:

import { AlertController } from 'ionic-angular';

export class MyPage {
  constructor(public alertCtrl: AlertController) {
  }

what does that : in alertCtrl: AlertController means?

Possible duplicate of [What does this symbol mean in JavaScript?](http://stackoverflow.com/questions/9549780/what-does-this-symbol-mean-in-javascript) which has a link to a question reguarding the specific symbol: http://stackoverflow.com/questions/39655737/javascript-strange-syntax-that-works-but-how — Tot Zam, Dec 06 '16 at 05:00
possible duplicate of http://stackoverflow.com/questions/418799/what-does-colon-do-in-javascript — Jayanti Lal, Dec 06 '16 at 05:02

score 3 · Accepted Answer · edited Dec 06 '16 at 06:16

3

The : in typescript means type assignment/annotation...

alertCtrl: AlertController means declare alertCtrl as AlertController, which will only accept Objects of AlertController type.

count:number means declare count as number, which will only accept number.

name:string means declare name as string, which will only accept a string.

edited Dec 06 '16 at 06:16

eko

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answered Dec 06 '16 at 05:06

coderdark

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score 0 · Answer 2 · answered Dec 06 '16 at 08:23

The code is written in TypeScript, which is a language that is compiled to JavaScript.

The : symbol is used to specify typing. It can come after a variable declaration to specify its type, after a function's parameter or after the function's heading to specify it's return type (which can be void).

Examples:

let a: number = 8;
function (b: number): number { return b; }

What does the symbol ":" mean in Javascript?

2 Answers2