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How to check null or empty or undefined in Angular?


null checking is a common validation that every developer needs to know.

In this tutorial, We are going to discuss how to check a null or empty, or undefined check-in Angular.

Angular uses Typescript as a programming language, Since typescript is strongly typed so We are going to discuss multiple ways to check null

We are going to discuss multiple ways

  • Checking null in Angular template HTML component
  • Checking null in Angular typescript component
  • Angular check for Array is empty or null or undefined
  • Angular check for the object is null or undefined
  • Angular ngIf null check

How to check if a variable string is empty or undefine or null in Angular

This example checks a variable of type string or object checks

  • Angular typescript component
  • Template HTML component

Typescript component, Written a function for checking null or undefined, or empty using the typeOf operator It is check for undefined values and returns true if it is null

isNameCheck(): boolean {
    if (typeof this.stringValue != 'undefined' && this.stringValue) {
      return false;
    }
    return true;
  }

Here is a complete Angular component example

import { Component, VERSION } from '@angular/core';

@Component({
  selector: 'my-app',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css']
})
export class AppComponent {
  stringValue = null;

  isNameCheck(): boolean {
    if (typeof this.stringValue != 'undefined' && this.stringValue) {
      return false;
    }
    return true;
  }
}

In template HTML component:

We can use the ngIf directive to check empty null or undefined.

In this example, if stringValue is empty or null, or undefined, It prints the empty message.

stringValue can be number or string or array or object

<div *ngIf="stringValue">
  <span>stringValue is not empty</span>
</div>

<div *ngIf="!stringValue">
  <span>stringValue is empty.</span>
</div>
{{isNameCheck()}}

NgIf array is empty check-in Angular

ngIf checks an array using length and returns the length of an array.

The below code is checked below things.

  • myArray is empty or not used? operator
  • if myArray is not null, It checks for the length property
<div *ngIf="!myArray?.length ">
  <span>Array is empty</span>
</div>
<div *ngIf="myArray?.length ">
  <span>
    Array is not empty
  </span>
</div>

Check if an object is empty in Angular

In the typescript component, We can check using the custom function which checks if there are no properties in An object.

import { Component, VERSION } from '@angular/core';

@Component({
  selector: 'my-app',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css']
})
export class AppComponent {
  stringValue = null;

  myArray = [];


  isObjectCheck(obj: any): boolean {
    for (var key in this) {
      if (this.hasOwnProperty(key)) return false;
    }
    return true;
  }
}
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