how to check type of variable in typescript +angular?

Question

could you please tell me how to check typeof of variable in typescript + angular ?

import { Component } from '@angular/core';  interface Abc {   name : string } @Component({   selector: 'my-app',   templateUrl: './app.component.html',   styleUrls: [ './app.component.css' ] }) export class AppComponent  {   name = 'Angular 6';   a:Abc= {   name:"sss"   }    constructor(){     console.log(typeof this.a)    // console.log(this.a instanceof Abc)    } } 

It should give true and false

https://stackblitz.com/edit/angular-jfargi?file=src/app/app.component.ts

Answer 1

Interfaces are erased at runtime so there will be no trace of the interface in any runtime call. You can either use a class instead of an interface (classes exist at runtime and obey instanceof

class Abc {     private noLiterals: undefined;     constructor(public name: string) { } } @Component({     selector: 'my-app',     templateUrl: './app.component.html',     styleUrls: ['./app.component.css'] }) export class AppComponent {     name = 'Angular 6';     a: Abc = new Abc( "sss")      constructor() {         console.log(this.a instanceof Abc) // Will be true      } } 

Or you can do structural checking to see if the properties of Abc are present at runtime in the object:

export class AppComponent {     name = 'Angular 6';     a: Abc = { name: "sss" }      constructor() {         console.log('name' in this.a) // Will be true      } } 

Answer 2

just use typeof(variable); so in your case:

console.log(typeof(this.a));