How Can I Efficiently Extend a JavaScript Array with Another Array?

Extending JavaScript Array with Another Array

Extending an existing JavaScript array with another array is not a direct operation. However, there are efficient ways to achieve this without creating a new array.

Push Method with Spread Operator (ES6)

The .push method can accept multiple arguments. Using the spread operator, we can pass all elements of the second array as arguments to .push, thus extending the first array:

a.push(...b)

For browsers that don't support ES6, we can use .apply instead:

a.push.apply(a, b)

Alternatively, for clarity:

Array.prototype.push.apply(a,b)

Loop-Based Technique

A loop-based approach is recommended if the second array (b) is large, as the previous methods can cause stack overflow errors. The following code performs the extension operation:

for (var i = 0; i < b.length; i++) {
  a.push(b[i]);
}

Further Considerations

Note that both approaches will work efficiently when a is significantly larger than b. However, if b contains a large number of elements, the loop-based technique should be used to avoid stack overflow errors.

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