Iterator

The Iterator function returns an object which implements legacy iterator protocol and iterates over enumerable properties of an object.

Syntax

Iterator(object, [keyOnly])

Parameters

object

Object to iterate over properties.

keyOnly

If keyOnly is truthy value, Iterator.prototype.next returns property_name only.

Description

Returns Iterator instance that iterates over object. Iterator instance returns [property_name, property_value] array for each iteration if keyOnly is falsy,  otherwise, if keyOnly is truthy, it returns property_name for each iteration.  If object is the Iterator instance or Generator instance, it returns object itself.

Properties

Iterator.prototype[@@iterator]

Returns a function that returns iterator object, that conforms to iterator protocol.

Methods

Iterator.prototype.next

Returns next item in the [property_name, property_value] format or property_name only. It throws StopIteration if there are no more items.

Examples

Iterating over properties of an object

var a = {
  x: 10,
  y: 20,
};
var iter = Iterator(a);
console.log(iter.next()); // ["x", 10]
console.log(iter.next()); // ["y", 20]
console.log(iter.next()); // throws StopIteration

Iterating over properties of an object with legacy destructuring for-in statement

var a = {
  x: 10,
  y: 20,
};
for (var [name, value] in Iterator(a)) {
  console.log(name, value);   // x 10
                              // y 20
}

Iterating with for-of

var a = {
  x: 10,
  y: 20,
};
for (var [name, value] of Iterator(a)) {  // @@iterator is used
  console.log(name, value);   // x 10
                              // y 20
}

Iterates over property name

var a = {
  x: 10,
  y: 20,
};
for (var name in Iterator(a, true)) {
  console.log(name);   // x
                       // y
}

Passing Generator instance

function* f() {
  yield 'a';
  yield 'b';
}
var g = f();
console.log(g == Iterator(g)); // true
for (var v in Iterator(g)) {
  console.log(v);   // a
                    // b
}

Passing Iterator instance

var a = {
  x: 10,
  y: 20,
};
var i = Iterator(a);
console.log(i == Iterator(i)); // true

Specifications

Non-standard. Not part of any current standards document.

Browser compatibility

See also

• Iterators and Generators
• StopIteration