what is the best way to determine the variable type in typescript and angular?

Question

what is the best way to determine the variable type in typescript and angular?

How can I determine the type of a variable in TypeScript with 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) 
  }
}

This code snippet should provide results of true and false

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angular typescript

Answer 1

Answer №1

Runtime erases interfaces, leaving no trace of them in function calls. To work around this, you can opt for using classes instead of interfaces since classes are present at runtime and adhere to 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 return true 
    }
}

Alternatively, you can perform structural checks to verify if the properties of Abc exist at runtime in the object:

export class AppComponent {
    name = 'Angular 6';
    a: Abc = { name: "sss" }

    constructor() {
        console.log('name' in this.a) // Will return true 
    }
}

Answer 2

Runtime erases interfaces, leaving no trace of them in function calls. To work around this, you can opt for using classes instead of interfaces since classes are present at runtime and adhere to 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 return true 
    }
}

Alternatively, you can perform structural checks to verify if the properties of Abc exist at runtime in the object:

export class AppComponent {
    name = 'Angular 6';
    a: Abc = { name: "sss" }

    constructor() {
        console.log('name' in this.a) // Will return true 
    }
}

Answer 3

Answer №2

To check the type of a variable, simply utilize typeof(variableName);. In your situation, it would look like this:

console.log(typeof(exampleVariable));

Answer 4

To check the type of a variable, simply utilize typeof(variableName);. In your situation, it would look like this:

console.log(typeof(exampleVariable));

Answer 5

Answer №3

Use 'instanceof' or 'is':

a instanceof Abc;

For more information, check out: Class type check with typescript

Answer 6

Use 'instanceof' or 'is':

a instanceof Abc;

For more information, check out: Class type check with typescript

Answer 7

Answer №4

When dealing with primitive data types such as strings or numbers, you can verify the type like so:

if( typeof(your_variable) === 'string' ) { ... }

Answer 8

When dealing with primitive data types such as strings or numbers, you can verify the type like so:

if( typeof(your_variable) === 'string' ) { ... }

Answer 9

Answer №5

At compile-time, interfaces are present but they are removed after compilation, which means the code will not have any effect at run-time and will always return false if you try to execute it.

If you're curious, take a look here -

constructor(){
    console.log(typeof(this.a), '---');
    console.log(this.instanceOfA(this.a)); 
  }

  instanceOfA(object: any): object is ABc {
    return 'member' in object;
  }

See a Working Example

To dive deeper into this topic, check out -

Answer 10

At compile-time, interfaces are present but they are removed after compilation, which means the code will not have any effect at run-time and will always return false if you try to execute it.

If you're curious, take a look here -

constructor(){
    console.log(typeof(this.a), '---');
    console.log(this.instanceOfA(this.a)); 
  }

  instanceOfA(object: any): object is ABc {
    return 'member' in object;
  }

See a Working Example

To dive deeper into this topic, check out -

Answer 11

Answer №6

give this a shot

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

testing out how to determine the type of a variable, such as string, number, or object, among others

  if((typeof (this.specialProviderSelected)) === 'string') {
     reacting accordingly...
    }
   if((typeof (this.specialProviderSelected))  === 'number') {
     reacting accordingly...
    }
    if((typeof (this.specialProviderSelected))  === 'object') {
     reacting accordingly...
    }

Answer 12

give this a shot

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

testing out how to determine the type of a variable, such as string, number, or object, among others

  if((typeof (this.specialProviderSelected)) === 'string') {
     reacting accordingly...
    }
   if((typeof (this.specialProviderSelected))  === 'number') {
     reacting accordingly...
    }
    if((typeof (this.specialProviderSelected))  === 'object') {
     reacting accordingly...
    }

what is the best way to determine the variable type in typescript and angular?

Answer №1

Answer №2

Answer №3

Answer №4

Answer №5

See a Working Example

Answer №6

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