What is the importance of interruption in underscore.js?

Question

In underscore.js have the following code:

if (iterator.call(context, obj[keys[i]], keys[i], obj) === breaker) return;

for example, in "every" function

var each = _.each = _.forEach = function(obj, iterator, context) {
  if (obj == null) return;
  if (nativeForEach && obj.forEach === nativeForEach) {
    obj.forEach(iterator, context);
  } else if (obj.length === +obj.length) {
    for (var i = 0, length = obj.length; i < length; i++) {
      if (iterator.call(context, obj[i], i, obj) === breaker) return;
    }
  } else {
    var keys = _.keys(obj);
    for (var i = 0, length = keys.length; i < length; i++) {
      if (iterator.call(context, obj[keys[i]], keys[i], obj) === breaker) return;
    }
  }
};

I don’t understand why add this if(xxx === breaker) return;? When will it be iterator.call(context, obj[keys[i]], keys[i], obj) === breaker?

Answer 1

From annotated source code ,

Establish the object that gets returned to break out of a loop iteration.

This is just a control value, and if the iterator function returns breaker, it _.eachwill immediately return. Since breakerit is not assigned to any other object, no other object can be equal breaker(it maps to ===). It is used internally _.everyand _.any.

_.every

if (!(result = result && iterator.call(context, value, index, list))) return breaker;

_.any

if (result || (result = iterator.call(context, value, index, list))) return breaker;

breaker, _.each .

Answer 2

_underscore, _.all(), _.every(), _.any(), _.each() , breaker, (.. , ..)

Answer 3

, :

var breaker = {};

, , , (iterator) . , "" .