CODEWITHSUNDEEP
javascriptarrays
Voice Of The Rain
Voice Of The Rain

Reputation: 587

Push an empty element into javascript array

How can I push empty element to an existing Js array, lets assume :

var arr = [54,77,21];
var target = [54,77,21,,,,36];
arr.push(); //do not append an empty element into the array.
arr.push();

console.log(JSON.stringify(arr)); //output: [54,77,21]

How to append empty elements so "arr" will be equivalent to "target" array?

Upvotes: 10

Views: 43434

Answers (3)

Wali Waqar
Wali Waqar

Reputation: 385

You could use the array.prototype.concat() method.

    var arr1 = [1, 2, 3, 4];

    var arrtarget = [1, 2, 3, 4, , , , 5, 6];

    console.log(arr1);
    console.log(arrtarget);

    newArr = arr1.concat([, , , 5,6]);

    console.log(newArr);

Alternatively, you could use the Array.Prototype.push() method as

arr1.push(undefined);

Upvotes: 1

Nina Scholz
Nina Scholz

Reputation: 386560

You could address the index directly. This builds a sparse array.

var arr = [54,77,21];

arr[6] = 36;
console.log(JSON.stringify(arr));

Or push undefined until you like to push the value. This returns a filled array.

var arr = [54,77,21];

arr.push(undefined);
arr.push(undefined);
arr.push(undefined);
arr.push(36);
console.log(JSON.stringify(arr));

By using JSON.stringify, you get for undefined or sparse items null, because JSON knows only null instead of undefined.

Upvotes: 9

str
str

Reputation: 44969

You can use Array#length:

arr.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; for example, if you set length to 3 when it is currently 2, the array now contains 3 elements, which causes the third element to be a non-iterable empty slot.

But note that JSON does not support sparse arrays. I.e. you cannot see empty slots with JSON.stringify.

var arr = [54,77,21];
arr.length++;
arr.length++;
arr.length++;
arr.push(36);
console.log(arr);

(FYI: Stack Snippets do not seem to support sparse arrays correctly. You need to run that code in the browser console instead.)

Upvotes: 6

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