CODE EXAMPLE FOR JAVASCRIPT

javascript break out of map

// You cannot break out of `Array.protoype.map`.

/*
Map is essentially a for loop that applies a
function to each value of an array and pushes it
to a new array.
*/

// A simple recreation of `Array.prototype.map`:
Array.prototype.map = function(callbackfn) {
	const result = [];
	for (let i = 0; i < this.length; i++) {
		result.push(callbackfn(result, i, this));
	}
	return result;
};

/*
Essentially, you can just create a new array and
use a for loop which you can break from:
*/
const arr = [ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 ];

const arrX2 = [];
for (let i = 0; i < arr.length; i++) {
	if (i >= 5) {
		break;
	}
	arrX2.push(arr[i] * 2);
}

/*
Although if you are 100% set on 'breaking' from
`Array.prototype.map`, you could customise the
function to suit you. Have a look at this example:
*/
Array.prototype.map = function(callbackfn) {
	const result = [];
	let _break = false;
	function breakFunc() { _break = true; }
		for (let i = 0; i < this.length; i++) {
			/*
			we need to store the item so we don't
			automatically push undefined to the
			array if the break function is
			called.
			*/
			const item = callbackfn(this[i], i, this, breakFunc);
			if (_break) {
				return result;
			}
			result.push(item);
	}
	return result;
};

const arr = [ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 ];

const arrX2 = arr.map((item, index, array, fakeBreak) => index >= 5 ? fakeBreak() : item);

/*
You could create your own custom `Array.prototype.map`
like the one above if you really wanted, but it is
probably better to just use a normal for loop.
*/