JavaScript操作符与表达式详解：从基础语法到高级用法

let Employee = {
   age: 28,
   name: 'abc',
   designation: 'developer'
 };
 console.log(delete Employee.name);  // returns true
 console.log(delete Employee.age);  // returns true
 console.log(Employee); //{designation: "developer"}

typeof NaN === 'number';
typeof Number(1) === 'number';
typeof "" === 'string';
typeof true === 'boolean';
typeof Symbol('foo') === 'symbol';
typeof undefined === 'undefined';
typeof null === 'object'
typeof [1, 2, 4] === 'object';
typeof new Boolean(true) === 'object';
typeof new Number(1) === 'object';
typeof new String("abc") === 'object';
typeof function(){} === 'function';

<a href="javascript:void(0);" rel="external nofollow" >
 这个链接点击之后不会做任何事情，如果去掉 void()，
 点击之后整个页面会被替换成一个字符 0。
</a>
<p> chrome中即使<a href="javascript:0;" rel="external nofollow" >也没变化，firefox中会变成一个字符串0 </p>
<a href="javascript:void(document.body.style.backgroundColor='green');" rel="external nofollow" >
 点击这个链接会让页面背景变成绿色。
</a>

let trees = new Array("redwood", "bay", "cedar", "oak", "maple");
console.log(0 in trees); // 返回true
console.log(3 in trees); // 返回true
console.log(6 in trees); // 返回false
console.log("bay" in trees); // 返回false (必须使用索引号,而不是数组元素的值)
console.log("length" in trees); // 返回true (length是一个数组属性)

let simpleStr = "This is a simple string";
let myString = new String();
let newStr  = new String("String created with constructor");
let myDate  = new Date();
let myObj   = {};
simpleStr instanceof String; // 返回 false, 检查原型链会找到 undefined
myString instanceof String; // 返回 true
newStr  instanceof String; // 返回 true
myString instanceof Object; // 返回 true
myDate instanceof Date;   // 返回 true
myObj instanceof Object;  // 返回 true, 尽管原型没有定义

function f2(){
 "use strict"; // 这里是严格模式
 return this;
}
f2() === undefined; // true

function add(c, d) {
 return this.a + this.b + c + d;
}
let o = {a: 1, b: 3};
// 第一个参数是作为‘this'使用的对象
// 后续参数作为参数传递给函数调用
add.call(o, 5, 7); // 1 + 3 + 5 + 7 = 16

function f(){
 return this.a;
}
let g = f.bind({a:"azerty"});
console.log(g()); // azerty
let h = g.bind({a:'yoo'}); // bind只生效一次！
console.log(h()); // azerty

let globalObject = this;
let foo = (() => this);
console.log(foo() === globalObject); // true

class Human {
 constructor() {}
 static ping() {
  return 'ping';
 }
}
 
class Computer extends Human {
 constructor() {}
 static pingpong() {
  return super.ping() + ' pong';
 }
}
Computer.pingpong(); // 'ping pong'

function Car() {}
car1 = new Car()
console.log(car1.color)      // undefined
Car.prototype.color = null
console.log(car1.color)      // null
car1.color = "black"
console.log(car1.color)      // black

function myFunction(x, y, z) { }
let args = [0, 1, 2];
myFunction.apply(null, args);
 
//展开语法
function myFunction(x, y, z) { }
let args = [0, 1, 2];
myFunction(...args);

let parts = ['shoulders'，'knees']; 
let lyrics = ['head'，... parts，'and'，'toes']; 
// ["head", "shoulders", "knees", "and", "toes"]

let arr = [1, 2, 3];
let arr2 = [...arr]; // like arr.slice()
arr2.push(4); 
 
// arr2 此时变成 [1, 2, 3, 4]
// arr 不受影响

let arr1 = [0, 1, 2];
let arr2 = [3, 4, 5];
// 将 arr2 中所有元素附加到 arr1 后面并返回
let arr3 = arr1.concat(arr2);
 
//使用展开语法
let arr1 = [0, 1, 2];
let arr2 = [3, 4, 5];
let arr3 = [...arr1, ...arr2];

let Foo = class {
 constructor() {}
 bar() {
  return "Hello World!";
 }
};
let instance = new Foo();
instance.bar(); 
// "Hello World!"

/* 函数声明 */
 
foo(); // "bar"
function foo() {
 console.log("bar");
}
 
 
/* 函数表达式 */
 
baz(); // TypeError: baz is not a function
let baz = function() {
 console.log("bar2");
};

function* idMaker(){
 let index = 0;
 while(index<3)
  yield index++;
}
 
let gen = idMaker();
console.log(gen.next().value); // 0
console.log(gen.next().value); // 1
console.log(gen.next().value); // 2
console.log(gen.next().value); // undefined

function* idMaker(){
  let index = arguments[0] || 0;
  while(true)
    yield index++;
}
 
let gen = idMaker(5);
console.log(gen.next().value); // 5
console.log(gen.next().value); // 6

function *createIterator() {
  let first = yield 1;
  let second = yield first + 2; // 4 + 2 
                 // first =4 是next(4)将参数赋给上一条的
  yield second + 3;       // 5 + 3
}
 
let iterator = createIterator();
 
console.log(iterator.next());  // "{ value: 1, done: false }"
console.log(iterator.next(4));  // "{ value: 6, done: false }"
console.log(iterator.next(5));  // "{ value: 8, done: false }"
console.log(iterator.next());  // "{ value: undefined, done: true }"

let x = function*(y) {
  yield y * y;
};