ECMAScript 6 扫盲

var a = 2;
{
  let a = 3;
  console.log(a); // 3
}
console.log(a); // 2

{
  const ARR = [5,6];
  ARR.push(7);
  console.log(ARR); // [5,6,7]
  ARR = 10; // TypeError
}

var getPrice = function() {
  return 4.55;
};
 
// Implementation with Arrow Function
var getPrice = () => 4.55;

1 let arr = ['apple', 'banana', 'orange'];
2  
3 let breakfast = arr.map(fruit => {
4   return fruit + 's';
5 });
6  
7 console.log(breakfast); // apples bananas oranges

1 function Person() {
2   this.age = 0;
3  
4   setInterval(function growUp() {
5     // 在非严格模式下，growUp() 函数的 this 指向 window 对象
6     this.age++;
7   }, 1000);
8 }
9 var person = new Person();

1 function Person() {
2   var self = this;
3   self.age = 0;
4  
5   setInterval(function growUp() {
6     self.age++;
7   }, 1000);
8 }

1 let getFinalPrice = (price, tax=0.7) => price + price * tax;
2 getFinalPrice(500); // 850

1 function foo(x,y,z) {
2   console.log(x,y,z);
3 }
4  
5 let arr = [1,2,3];
6 foo(...arr); // 1 2 3

1 let oValue = 0o10;
2 console.log(oValue); // 8
3  
4 let bValue = 0b10; // 二进制使用 `0b` 或者 `0B`
5 console.log(bValue); // 2

 1 var parent = {
 2   foo() {
 3     console.log("Hello from the Parent");
 4   }
 5 }
 6  
 7 var child = {
 8   foo() {
 9     super.foo();
10     console.log("Hello from the Child");
11   }
12 }
13  
14 Object.setPrototypeOf(child, parent);
15 child.foo(); // Hello from the Parent
16              // Hello from the Child

1 let nicknames = ['di', 'boo', 'punkeye'];
2 nicknames.size = 3;
3 for (let nickname in nicknames) {
4   console.log(nickname);
5 }
6 Result: 0, 1, 2, size

 1 var myMap = new Map();
 2  
 3 var keyString = "a string",
 4     keyObj = {},
 5     keyFunc = function () {};
 6  
 7 // 设置值
 8 myMap.set(keyString, "value 与 'a string' 关联");
 9 myMap.set(keyObj, "value 与 keyObj 关联");
10 myMap.set(keyFunc, "value 与 keyFunc 关联");
11  
12 myMap.size; // 3
13  
14 // 获取值
15 myMap.get(keyString);    // "value 与 'a string' 关联"
16 myMap.get(keyObj);       // "value 与 keyObj 关联"
17 myMap.get(keyFunc);      // "value 与 keyFunc 关联"

 1 let w = new WeakMap();
 2 w.set('a', 'b'); 
 3 // Uncaught TypeError: Invalid value used as weak map key
 4  
 5 var o1 = {},
 6     o2 = function(){},
 7     o3 = window;
 8  
 9 w.set(o1, 37);
10 w.set(o2, "azerty");
11 w.set(o3, undefined);
12  
13 w.get(o3); // undefined, because that is the set value
14  
15 w.has(o1); // true
16 w.delete(o1);
17 w.has(o1); // false

1 let mySet = new Set([1, 1, 2, 2, 3, 3]);
2 mySet.size; // 3
3 mySet.has(1); // true
4 mySet.add('strings');
5 mySet.add({ a: 1, b:2 });

 1 mySet.forEach((item) => {
 2   console.log(item);
 3     // 1
 4     // 2
 5     // 3
 6     // 'strings'
 7     // Object { a: 1, b: 2 }
 8 });
 9  
10 for (let value of mySet) {
11   console.log(value);
12     // 1
13     // 2
14     // 3
15     // 'strings'
16     // Object { a: 1, b: 2 }
17 }

 1 var ws = new WeakSet();
 2 var obj = {};
 3 var foo = {};
 4  
 5 ws.add(window);
 6 ws.add(obj);
 7  
 8 ws.has(window); // true
 9 ws.has(foo);    // false, foo 没有添加成功
10  
11 ws.delete(window); // 从结合中删除 window 对象
12 ws.has(window);    // false, window 对象已经被删除

 1 class Task {
 2   constructor() {
 3     console.log("task instantiated!");
 4   }
 5  
 6   showId() {
 7     console.log(23);
 8   }
 9  
10   static loadAll() {
11     console.log("Loading all tasks..");
12   }
13 }
14  
15 console.log(typeof Task); // function
16 let task = new Task(); // "task instantiated!"
17 task.showId(); // 23
18 Task.loadAll(); // "Loading all tasks.."

class Car {
  constructor() {
    console.log("Creating a new car");
  }
}
 
class Porsche extends Car {
  constructor() {
    super();
    console.log("Creating Porsche");
  }
}
 
let c = new Porsche();
// Creating a new car
// Creating Porsche

1 var sym = Symbol( "some optional description" );
2 console.log(typeof sym); // symbol

1 var o = {
2     val: 10,
3     [ Symbol("random") ]: "I'm a symbol",
4 };
5  
6 console.log(Object.getOwnPropertyNames(o)); // val

 1 function *infiniteNumbers() {
 2   var n = 1;
 3   while (true){
 4     yield n++;
 5   }
 6 }
 7  
 8 var numbers = infiniteNumbers(); // returns an iterable object
 9  
10 numbers.next(); // { value: 1, done: false }
11 numbers.next(); // { value: 2, done: false }
12 numbers.next(); // { value: 3, done: false }

1 var p = new Promise(function(resolve, reject) {  
2   if (/* condition */) {
3     // fulfilled successfully
4     resolve(/* value */);  
5   } else {
6     // error, rejected
7     reject(/* reason */);  
8   }
9 });

1 p.then((val) => console.log("Promise Resolved", val),
2        (err) => console.log("Promise Rejected", err));