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Generator

Generator functions can be paused, returned, and resumed, comparable to the StartCoroutine() function in Unity.Calling a generator function returns an iterator.


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<!DOCTYPE html><html><body><script>

function* idMaker(){
   var index = 0;
   while(true) yield index++;}var gen = idMaker();console.log(gen.next().value); // 0console.log(gen.next().value); // 1console.log(gen.next().value); // 2

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Arguments can be passed into the iterator.


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<!DOCTYPE html><html><body><script>

function* logGenerator() {
  console.log(yield); console.log(yield); console.log(yield);}var gen = logGenerator();gen.next(); gen.next(1); // 1gen.next(2); // 2gen.next(3); // 3

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'return'prevents the generator from resuming.


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<!DOCTYPE html><html><body><script>

function* gf() {
  yield 1;
  return 2;
  yield 3;}var gen = gf();console.log(gen.next()); // {value: 1, done: false}console.log(gen.next()); // {value: 2, done: true}console.log(gen.next()); // {value: undefined, done: true}

</script></body><html>

To nest generators, use yield *yield * yield * instead.


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<!DOCTYPE html><html><body><script>

function* anotherGenerator(i) {
  yield i + 1;
  yield i + 2;}function* generator(i) {
  yield i;
  yield* anotherGenerator(i);
  yield i + 10;}var g = generator(10);console.log(g.next().value); // 10console.log(g.next().value); // 11console.log(g.next().value); // 12console.log(g.next().value); // 20

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Generators are not constructable.


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<!DOCTYPE html><html><body><script>

function* f() {}var obj = new f; // throws "TypeError: f is not a constructor"

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To tell if a function is a generator function:


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<!DOCTYPE html><html><body><script>

function isGenerator(fn) { return fn.constructor.name === 'GeneratorFunction';}function f(){}function* g(){}console.log(isGenerator(f));  // falseconsole.log(isGenerator(g));  // trueconsole.log(g instanceof (function*(){}).constructor); //true

</script></body><html>