create - How do I empty an array in JavaScript?




javascript empty (12)

To Empty a Current memory location of an array use: 'myArray.length = 0' or 'myArray.pop() UN-till its length is 0'

  • length : You can set the length property to truncate an array at any time. When you extend an array by changing its length property, the number of actual elements increases.
  • pop() : The pop method removes the last element from an array and returns that returns the removed value.
  • shift() : The shift method removes the element at the zeroeth index and shifts the values at consecutive indexes down, then returns the removed value.

Example:

var arr = ['77'];
arr.length = 20;
console.log("Increasing : ", arr); // (20) ["77", empty × 19]
arr.length = 12;
console.log("Truncating : ", arr); // (12) ["77", empty × 11]

var mainArr = new Array();
mainArr = ['1', '2', '3', '4'];

var refArr = mainArr;
console.log('Current', mainArr, 'Refered', refArr);

refArr.length = 3;
console.log('Length: ~ Current', mainArr, 'Refered', refArr);

mainArr.push('0');
console.log('Push to the End of Current Array Memory Location \n~ Current', mainArr, 'Refered', refArr);

mainArr.poptill_length(0);
console.log('Empty Array \n~ Current', mainArr, 'Refered', refArr);

Array.prototype.poptill_length = function (e) {
  while (this.length) {
    if( this.length == e ) break;

    console.log('removed last element:', this.pop());
  }
};

  • new Array() | [] Create an Array with new memory location by using Array constructor or array literal.

    mainArr = []; // a new empty array is addressed to mainArr.
    
    var arr = new Array('10'); // Array constructor
    arr.unshift('1'); // add to the front
    arr.push('15'); // add to the end
    console.log("After Adding : ", arr); // ["1", "10", "15"]
    
    arr.pop(); // remove from the end
    arr.shift(); // remove from the front
    console.log("After Removing : ", arr); // ["10"]
    
    var arrLit = ['14', '17'];
    console.log("array literal « ", indexedItem( arrLit ) ); // {0,14}{1,17}
    
    function indexedItem( arr ) {
        var indexedStr = "";
        arr.forEach(function(item, index, array) {
            indexedStr += "{"+index+","+item+"}";
            console.log(item, index);
        });
        return indexedStr;
    }
    
  • slice() : By using slice function we get an shallow copy of elements from the original array, with new memory address, So that any modification on cloneArr will not affect to an actual|original array.

    var shallowCopy = mainArr.slice(); // this is how to make a copy
    
    var cloneArr = mainArr.slice(0, 3); 
    console.log('Main', mainArr, '\tCloned', cloneArr);
    
    cloneArr.length = 0; // Clears current memory location of an array.
    console.log('Main', mainArr, '\tCloned', cloneArr);
    

Is there a way to empty an array and if so possibly with .remove()?

For instance,

A = [1,2,3,4];

How can I empty that?


A.splice(0);

I just did this on some code I am working on. It cleared the array.


A more cross-browser friendly and more optimal solution will be to use the splice method to empty the content of the array A as below:

A.splice(0, A.length);


I'm surprised no one has suggested this yet:

let xs = [1,2,3,4];
for (let i in xs)
    delete xs[i];

This yields an array in quite a different state from the other solutions. In a sense, the array has been 'emptied':

xs
=> Array [ <4 empty slots> ]

[...xs]
=> Array [ undefined, undefined, undefined, undefined ]

xs.length
=> 4

xs[0]
=> ReferenceError: reference to undefined property xs[0]

You can produce an equivalent array with [,,,,] or Array(4)


If you need to keep the original array because you have other references to it that should be updated too, you can clear it without creating a new array by setting its length to zero:

A.length = 0;

If you use constants then you have no choice:

const numbers = [1, 2, 3]

You can not reasign:

numbers = []

You can only truncate:

numbers.length = 0


The answers that have no less that 2739 upvotes by now are misleading and incorrect.

The question is: "How do you empty your existing array?" E.g. for A = [1,2,3,4].

  1. Saying "A = [] is the answer" is ignorant and absolutely incorrect. [] == [] is false.

    This is because these two arrays are two separate, individual objects, with their own two identities, taking up their own space in the digital world, each on its own.


Let's say your mother asks you to empty the trash can.

  • You don't bring in a new one as if you've done what you've been asked for.
  • Instead, you empty the trash can.
  • You don't replace the filled one with a new empty can, and you don't take the label "A" from the filled can and stick it to the new one as in A = [1,2,3,4]; A = [];

Emptying an array object is the easiest thing ever:

A.length = 0;

This way, the can under "A" is not only empty, but also as clean as new!


  1. Furthermore, you are not required to remove the trash by hand until the can is empty! You were asked to empty the existing one, completely, in one turn, not to pick up the trash until the can gets empty, as in:

    while(A.length > 0) {
        A.pop();
    }
    
  2. Nor, to put your left hand at the bottom of the trash, holding it with your right at the top to be able to pull its content out as in:

    A.splice(0, A.length);
    

No, you were asked to empty it:

A.length = 0;

This is the only code that correctly empties the contents of a given JavaScript array.


Use a modified version of Jan's initial suggestion:

var originalLength = A.length;
for (var i = originalLength; i > 0; i--) {
     A.pop();
}

Use below if you need to empty Angular 2+ FormArray.

public emptyFormArray(formArray:FormArray) {
    for (let i = formArray.controls.length - 1; i >= 0; i--) {
        formArray.removeAt(i);
    }
}

You can add this to your JavaScript file to allow your arrays to be "cleared":

Array.prototype.clear = function() {
    this.splice(0, this.length);
};

Then you can use it like this:

var list = [1, 2, 3];
list.clear();

Or if you want to be sure you don't destroy something:

if (!Array.prototype.clear) {
    Array.prototype.clear = function() {
       this.splice(0, this.length);
    };
}

Lots of people think you shouldn't modify native objects (like Array), and I'm inclined to agree. Please use caution in deciding how to handle this.


You can easily create a function to do that for you, change the length or even add it to native Array as remove() function for reuse.

Imagine you have this array:

var arr = [1, 2, 3, 4, 5]; //the array

OK, just simply run this:

arr.length = 0; //change the length

and the result is:

[] //result

easy way to empty an array...

Also using loop which is not necessary but just another way to do that:

/* could be arr.pop() or arr.splice(0)
don't need to return as main array get changed */

function remove(arr) {
  while(arr.length) {
    arr.shift(); 
  }
}

There are also tricky way which you can think about, for example something like this:

arr.splice(0, arr.length); //[]

So if arr has 5 items, it will splice 5 items from 0, which means nothing will remain in the array.

Also other ways like simply reassign the array for example:

arr = []; //[]

If you look at the Array functions, there are many other ways to do this, but the most recommended one could be changing the length.

As I said in the first place, you can also prototype remove() as it's the answer to your question. you can simply choose one of the methods above and prototype it to Array object in JavaScript, something like:

Array.prototype.remove = Array.prototype.remove || function() {
  this.splice(0, this.length);
};

and you can simply call it like this to empty any array in your javascript application:

arr.remove(); //[]




arrays