The value of an Angular array seems to be disappearing after being copied to another array and then cleared

I have encountered an issue while working with arrays. I am initializing two arrays - one with some values and another as empty. However, when I assign the items from the first array to the second array and then clear the first array, it unexpectedly clears the second array as well.

My Code:

  array1: any = [1, 2, 3, 4, 5];
  array2: any = [];

  ngOnInit() {
    this.array2 = this.array1;
    this.array1.length = 0;

    console.log('I cleared Array1');
    console.log(this.array1);

    console.log('Array2 Clears Automatically');
    console.log(this.array2);
  }

Here is a Stackblitz sample demonstrating the issue: https://stackblitz.com/edit/angular-yfhdi3?file=src%2Fapp%2Fapp.component.ts

I need to find a solution to prevent the second array (array2) from losing its value after assignment, as I plan to perform operations on it later in the code.

Answer №1

When working with arrays in JavaScript, it's important to remember that they are objects. This means that assigning one array to another like this.array2 = this.array1 will make both variables point to the same object. As a result, any changes made to one variable will affect the other. To avoid this, use spread syntax to create a copy of the elements from array1 and assign them to array2. Here is an example using spread syntax (stackblitz):

this.array2 = [...this.array1];

Answer №2

Here is a helpful tip for you:

 numbers: any = [1, 2, 3, 4, 5];
  emptyArray: any = [];

  initializeArrays() {
    this.emptyArray.push(this.numbers);
    this.numbers =  [];

    console.log('The numbers array has been cleared');
    console.log(this.numbers);

    console.log('The emptyArray clears automatically');
    console.log(this.emptyArray);
  }

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