In-depth understanding of js generator data types and jsgenerator

In-depth understanding of js generator data types and jsgenerator

1. Overview

Generator is a new data type introduced by ES6. It looks like a function. In addition to return, yield can return multiple times.

Generator is defined by function * (note ),

2. Example

The function cannot save the status, and sometimes the global variable is required to save the number;

2.1

'Use strict '; function next_id () {var id = 1; while (id <100) {yield id; id ++;} return id;} // test: var x, pass = true, g = next_id (); for (x = 1; x <100; x ++) {if (g. next (). value! = X) {pass = false; alert ('test failed! '); Break ;}} if (pass) {alert (' test passed! ');}

2.2 an infinite loop iterator

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

2.3Generator.prototype.next ()

When the iteration ends, Generator. next (). done === true, Before the end = false

function* gen() {  yield 1; yield 2; yield 3;}var g = gen(); // "Generator { }"g.next();   // "Object { value: 1, done: false }"g.next();   // "Object { value: 2, done: false }"g.next();   // "Object { value: 3, done: false }"g.next();   // "Object { value: undefined, done: true }"

2.4 Generator. prototype. return ();

The return method returns the given parameter value and ends the iterator.

Example

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

Note: If the value of done is true, call return. The returned value is undefined.

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

2.5 Generator. prototype. throw ()

The thorw () method re-obtains the execution of the iterator by throwing an exception into the iterator;

Returns an object with two attributes: value and done.

function* gen() { while(true) {  try {    yield 42;  } catch(e) {   console.log("Error caught!");  } }}var g = gen();var a = g.next();// { value: 42, done: false }var b = g.throw(new Error("Something went wrong"));// "Error caught!"// { value: 42, done: false }console.log(a);console.log(b.value+"::"+b.done);

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