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How do I Empty an Array in JavaScript?

How do I Empty an Array in JavaScript?

Matthew C.

The ProblemJump To Solution

You want to empty an array in JavaScript. What are the different ways of doing this?

The Solution

There are several ways to clear an array. We’ll look at four methods.

Assign the Array to an Empty Array

The fastest and most straightforward way of emptying an array is by reassigning it to an empty array:

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let arr = [1, 2, 3, 4, 5]; arr = []; console.log(arr); // []

The array [1, 2, 3, 4, 5] is marked for garbage collection to free up memory as there is no reference to it after arr is reassigned. The array is not reachable anymore.

This method only works if the array is not a const variable, which can’t be changed by reassignment. If you change the above arr variable to a const variable, you’ll get the following error message:

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Assignment to constant variable.

If you use this method to empty an array, bear in mind that the empty array is newly created. If another variable or property references the array, that variable or property will still point to the original array, as can be seen in the code example below:

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let arr = [1, 2, 3, 4, 5]; const arr2 = arr; arr = []; console.log(arr); // [] console.log(arr2); // [1, 2, 3, 4, 5]

In JavaScript, objects are assigned and copied by reference, not by value. The variable arr2 does not copy the value of arr when it’s assigned to it. It stores the reference to the array, which is its address in memory.

Set the length property to 0

You can set the length property of an array to 0 to empty an array:

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arr.length = 0;

The array length property is readable and writable, so you can use it to get or set the length of an array.

Using the splice() Method

You can use the splice() method to change an array by modifying the array itself. You can use it to remove all elements in an array:

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arr.splice(0, arr.length);

The first argument, the start, is the index position at which to start changing the array. The second argument, the deleteCount, indicates the number of elements to remove in the array, starting from the start index position. The code above removes all elements in the array.

Using the pop() Method

You can also loop through an array and remove each element using the pop() or shift() methods, which remove the last element of an array and the first element of an array, respectively.

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while (arr.length > 0) { arr.pop(); }

This is the slowest of the methods described here.

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