Question

What is the best way to implement a simulation of a loop’s break statement, when one does iterate through a user/engine defined function?

forEach([0, 1, 2, 3, 4], function (n) {
  console.log(n);
  
  if (n === 2) {
    break;
  }
});

I’ve thought of implementing forEach in a way that would break when the function returns false. But I would like to hear thoughts on how that is normally done.

Answer 1

returning false is the most common way to do it. That’s what jQuery’s iterator function .each() does:

We can break the $.each() loop at a particular iteration by making the
callback function return false. Returning non-false is the same as a
continue statement in a for loop; it will skip immediately to the next
iteration.

And its very simplified implementation:

each: function( object, callback ) {
  var i = 0, length = object.length,
  for ( var value = object[0]; 
        i < length && callback.call( value, i, value ) !== false; // break if false is returned by the callback 
        value = object[++i] ) {}
  return object;
}