How to make another function aware of the loop name, so it can break it?

Question

You see I have this code. (https://jsfiddle.net/kg4f2bu0/).

Inside my iterate function I use a label for my loop, because I want to break it if it meets a condition. The condition gets checked inside the callback function. I want to break the for..of loop inside my callback function (compare). But it doesn't recognise the statement label. How can I make the callback function aware of the loop name?

This is JavaScript code. You can read information on label name here: https://javascript.info/while-for#labels-for-break-continue

const myArr = [1, 2, 3, 4, 5, 6];

const iterate = (arr, callback) => {
  search: for (const item of arr) {
    callback(item)
  }
}

const compare = (num) => {
  console.log(num);
  if (num === 4) {
    console.log("breaking");
    break search;
  }
}

iterate(myArr, compare)

Answer 1

You cannot break out of a loop from inside another function. The reason for this is technical: the label for the break is resolved once, before your code starts running. So at runtime, it's just a simple "goto"; the JavaScript engine doesn't go hunting up the call stack for a function containing a matching label. (What if there's none? What if there are multiple?)

What you can do instead is return a boolean value that indicates whether the item was found, and thus whether the loop should break:

const myArr = [1, 2, 3, 4, 5, 6];

const iterate = (arr, callback) => {
  for (const item of arr) {
    if (callback(item)) {
      break;
    }
  }
}

const compare = (num) => {
  console.log(num);
  if (num === 4) {
    console.log("breaking");
    return true;
  }
  return false;
}

iterate(myArr, compare)

Answer 2

Use Array.every() to perform the loop. As soon as False is returned, the looping ends. Here is an example.

const myArr = [1, 2, 3, 4, 5, 6];

const iterate = (arr, callback) => {
  search: arr.every(compare) 
}

const compare = (num) => {
  console.log(num);
  if (num === 4) {
    console.log("breaking");
    return false;
  }
  return true;
}

iterate(myArr, compare)