Question

[1,2,3].forEach(function(el) {
    if(el === 1) break;
});

How can I do this using the new forEach method in JavaScript? I’ve tried return;, return false; and break. break crashes and return does nothing but continue iteration.

Answer 1

There’s no built-in ability to break in forEach. To interrupt execution you would have to throw an exception of some sort. eg.

var BreakException = {};

try {
  [1, 2, 3].forEach(function(el) {
    console.log(el);
    if (el === 2) throw BreakException;
  });
} catch (e) {
  if (e !== BreakException) throw e;
}

JavaScript exceptions aren’t terribly pretty. A traditional for loop might be more appropriate if you really need to break inside it.

Use Array#some

Instead, use Array#some:

[1, 2, 3].some(function(el) {
  console.log(el);
  return el === 2;
});

This works because some returns true as soon as any of the callbacks, executed in array order, return true, short-circuiting the execution of the rest.

some, its inverse every (which will stop on a return false), and forEach are all ECMAScript Fifth Edition methods which will need to be added to the Array.prototype on browsers where they’re missing.

Use Array#every

[1, 2, 3].every(v => {
  if (v > 2) {
    return false // "break"
  }
  console.log(v);
  return true // must return true if doesn't break
});