JavaScript Set : Object

constructor iterable

Sets are a collection of Objects where each object can only appear once in the set.

ECMAScript 2015 Spec

Constructors

new Set() : Set

Creates an empty Set.

Example:

var x = new Set();
x.add(1);
x.add('a');
x.add({ foo: 'bar' });

for (var item of x) {
  console.dir(item);
}

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Results:

Spec

new Set(iterable : Object) : Set

Creates a Set by iterating over iterable and adding each value to the Set.

Example:

var fromArray = new Set([1, '1', { foo: 'bar' }]);

for (var item of fromArray) {
  console.dir(item);
}

var generator = function*() {
  yield 3;
  yield 'javascript';
};

var fromGenerator = new Set(generator());

for (var item of fromGenerator) {
  console.dir(item);
}

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Results:

Spec

Instance Properties

size : Number

The number of value in this.

Example:

var x = new Set(['a', 'b', 'c']);

console.log(x.size);

x.add('d');

console.log(x.size);

x.clear();

console.log(x.size);

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Results:

Spec

Instance Methods

add(value : Object) : Set

Stores value in this. If value is already stored, there is no change to the Set. Returns this.

Example:

var x = new Set(['a', 'b', 'c']);

console.log(x.has('a'));
console.log(x.has('d'));

x.add('d');
console.log(x.has('d'));

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Results:

Spec

clear() : undefined

Clears all values from this.

Example:

var x = new Set(['a', 'b', 'c']);

console.log(x.size);

x.clear();

console.log(x.size);

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Results:

Spec

delete(value : Object) : Boolean

Removes value* from this. Returns true if value was in this** before deleting it.

Example:

var x = new Set(['a', 'b', 'c']);

console.log('size before delete: ' + x.size);
console.log('deleted "a" = ' + x.delete('a'));

console.log('size after delete: ' + x.size);
console.log('deleted "foo" = ' + x.delete('foo'));

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Results:

Spec

entries() : Iterator

Returns an iterator of the items in this where the valuess of the iterator are of the form [value : Object, value : Object] (value is duplicated twice). See also keys() and values().

Example:

var x = new Set(['a', 'b', 'c']);

// Use for (... of ...) to loop over the iterator
for (var entry of x.entries()) {
  console.dir(entry);
}

// Or access the iterator manually
var entries = x.entries();

console.dir(entries.next());
console.dir(entries.next());
console.dir(entries.next());
console.dir(entries.next());

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Results:

Spec

forEach(callback : Function, [thisArg : Object]) : undefined

callback(value : Object, key : Object, set : Set) : undefined

Calls callback for each value in this. The Set passed to callback is the this of the call to forEach.

Example:

var x = new Set(['a', 'b', 'c']);

x.forEach(function(value) {
  console.dir(value);
});

Run

Results:

Spec

has(value : Object) : Boolean

Returns true if the set contains value.

Example:

var x = new Set(['a', 'b', 'c']);

console.log(x.has('a'));
console.log(x.has('foo'));

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Spec

keys() : Iterator

Same as values().

Spec

values() : Iterator

Returns an iterator of the values in this. The values function is also returned for this[Symbol.iterator] so you can iterate over this directly to get the values. See also entries() and keys().

Example:

var x = new Set(['a', 'b', 'c']);

// values is returned by x[Symbol.iterator] so you can just 
// use x directly in the for (... of ...) loop
for (var value of x) {
  console.dir(value);
}

// You can iterate over values explicitly
for (var value of x.values()) {
  console.dir(value);
}

// Or access the iterator manually
var values = x.values();

console.dir(values.next());
console.dir(values.next());
console.dir(values.next());
console.dir(values.next());

Run

Results:

Spec

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