How Can I Efficiently Extend a JavaScript Array In-Place Without Creating a New One?

Extending JavaScript Arrays Efficiently Without Creating a New Array

It's not uncommon to encounter scenarios where you want to extend an existing JavaScript array with another array without creating a new one. This can be useful to manipulate and combine data in a more efficient manner.

The Challenge

In JavaScript, extending an array doesn't have an explicit "extend" method like in Python. Instead, the concat method is typically used, but this creates a new array rather than modifying the existing one.

The Solution

To extend an existing array in place, you can leverage the push method, which has the ability to accept multiple arguments. By using the spread operator (...b), you can pass all the elements of the second array as individual arguments to push:

a.push(...b)

If your environment doesn't support this syntax, you can use the apply method of the Array object:

a.push.apply(a, b)

Note:

This solution may encounter stack overflow errors if the array to be added (b) is too long. If this is a potential concern, it's recommended to use a standard loop-based technique to extend the array.

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