Class
define
class Queue {
_queue;
constructor(contents = []) {
this._queue = [...contents];
}
pop() {
const value = this._queue[0];
this._queue.splice(0, 1);
return value;
}
extends
class PeekableQueue extends Queue {
peek() {
return this._queue[0];
}
class Account extends Foo {
constructor(balance) {
this.balance = balance;
}
history(done) {
someLongTask((err, data) => {
// Do something with data
done(null, data);
});
}
deposit(amount) {
this.balance += amount;
return this.balance;
}
}
// Currently, you can only declare functions in a class
Account.types = ['checking', 'savings'];
get,set
class Account {
constructor() {
this.balance = 0;
}
get underBudget() {
return this.balance >= 0;
}
get overBudget() {
return this.balance < 0;
}
}
const myAccount = Account();
myAccount.balance = 100;
console.log(myAccount.underBudget); // true
Iterable Class
可建立iterable class，並且可用generator建立iterator。
class MyIterable {
constructor(items) {
this.items = items;
}
*[Symbol.iterator]() {
for (let item of this.items) {
yield `Hello, ${item}`;
}
}
}
const test = new MyIterable([1, 2, 3, 4, 5]);
for (let item of test) {
console.log(item); // => Hello, 1...
}
Map
let map = new Map(arr);
for (let key of map.keys()) {
console.log(key);
}
for (let value of map.values()) {
console.log(value);
}
for (let item of map.entries()) {
console.log(item[0], item[1]
}
Module
基本定義與引用
用ES6 export，就用import；不要用require
一個文件中不要export與default export一起用
不要在import中使用*，確保module中有一個default export
//定義模組 module.js
var privateVar = "privateVar";
//不能被外部引用的成員
export var publicVar = "and this one is public";
//export出去，可被外部引用的成員
export function getVar() {
return privateVar;
};
//引用模組 use.js
import { getVar, publicVar } from 'mymodule';
//import getVar及publicVar兩個成員
console.log(getVar());
//一次引用這個模組的所有可引用成員
X import 'mm' from 'mymodule';
X import 'mymodule' as mm;
//或是這樣
import * as 'mm' from 'mymodule'; //不建議使用*
import abc =require('mymodule');
//不一定都有implement
import defaultMember from "module-name";
import * as name from "module-name";
import { member } from "module-name";
import { member as alias } from "module-name";
import { member1 , member2 } from "module-name";
import { member1 , member2 as alias2 , [...] } from "module-name";
import defaultMember, { member [ , [...] ] } from "module-name";
import defaultMember, * as name from "module-name";
import "module-name";
console.log(mm.gerVar());
default export(無命名export) (文件中只有一個成員)
//------ myFunc.js ------
export default function () { ... };
//------ main1.js ------
import myFunc from 'myFunc';
myFunc();
//------ MyClass.js ------
export default class { ... };
//------ main2.js ------
import MyClass from 'MyClass';
let inst = new MyClass();
一個文件中同時有export(一般export)與default export(無命名export)
//------ underscore.js ------
export default function (obj) {
...
};
export function each(obj, iterator, context) {
...
}
export { each as forEach };
//------ main.js ------
import _, { each } from 'underscore';
...
default export就是another named export
//以下兩者相同
import { default as foo } from 'lib';
import foo from 'lib';
//以下兩個模組export相同
//------ module1.js ------
export default 123;
//------ module2.js ------
const D = 123;
export { D as default };
commonJS的module
//------ underscore.js ------
var _ = function (obj) {
...
};
var each = _.each = _.forEach =
function (obj, iterator, context) {
...
};
module.exports = _;
//------ main.js ------
var _ = require('underscore');
var each = _.each;
...
//------ lib.js ------
var sqrt = Math.sqrt;
function square(x) {
return x * x;
}
function diag(x, y) {
return sqrt(square(x) + square(y));
}
module.exports = {
sqrt: sqrt,
square: square,
diag: diag,
};
//------ main.js ------
var square = require('lib').square;
var diag = require('lib').diag;
console.log(square(11)); // 121
console.log(diag(4, 3)); // 5
