摘要：對(duì)象只能在一行，不能多行模板字符串可以多行將字符串轉(zhuǎn)換成對(duì)象反序列化將對(duì)象轉(zhuǎn)換成字符串序列化會(huì)刪除一個(gè)字符串兩端的空白字符。并不影響原字符串本身，它返回的是一個(gè)新的字符串。

let ass="[{"name":"ss","age":"3"},{"name":"aa","age":"1"},{"name":"qq","age":"4"},{"name":"zz","age":"3"},{"name":"xx","age":"5"},{"name":"cc","age":"7"}]"

將JSON字符串轉(zhuǎn)換成JSON對(duì)象(JSON反序列化)
let aa=JSON.parse(ass);
console.log(aa[2].age);//4

將JSON對(duì)象轉(zhuǎn)換成JSON字符串(JSON序列化)
let arr=[
    {"name":"ss","age":"3"},
    {"name":"aa","age":"1"},
    {"name":"qq","age":"4"},
    {"name":"zz","age":"3"},
    {"name":"xx","age":"5"},
    {"name":"cc","age":"7"}
]
let bb=JSON.stringify(arr);
console.log(bb);//[{"name":"ss","age":"3"},{"name":"aa","age":"1"},{"name":"qq","age":"4"},{"name":"zz","age":"3"},{"name":"xx","age":"5"},{"name":"cc","age":"7"}]

會(huì)刪除一個(gè)字符串兩端的空白字符。并不影響原字符串本身，它返回的是一個(gè)新的字符串。
let str22="     fff    ";
console.log("+"+str22+"+");//+     fff    +
console.log("+"+str22.trim()+"+")//+fff+

//1970.7.1到現(xiàn)在，1秒=1000毫秒這個(gè)概率算
console.log(Date.now());//1500799156134
//toJSON()格林時(shí)間(德國(guó)) 與我們的時(shí)間正好相反
console.log(new Date().toJSON())//2017-07-23T08:42:13.050Z
console.log(new Date().toJSON().slice(0,10))//2017-07-23

小數(shù)后取位數(shù)，數(shù)字代表取到第幾位，四舍五入返回小數(shù)
let a=new Number(1.234);
console.log(a.toFixed(1));//1.2
let v=new Number(4.645372);
console.log(v.toFixed(2));//4.56
console.log(Math.round(13.89));//14 四舍五入返回整數(shù)

以指定的精度返回該數(shù)值對(duì)象的字符串表示。 precision 是 1 ~ 21 之間
let d=100000000000000000000;
console.log(d.toPrecision(7));1.000000e+20
console.log(d.toPrecision(3));1.00e+20

let arr=[1,2,3,4,5];
arr.forEach(function(value, index){
    console.log(value);//1,2,3,4,5
    console.log(index);//0,1,2,3,4
});

let arr1=arr.map(function(value){
    //return value+"abc";
    return value*2+1;
});
console.log(arr1);// ["1abc", "2abc", "3abc", "4abc", "5abc"]
console.log(arr1);//[3, 5, 7, 9, 11]

let arr2=arr.filter(function(value){
    return value>2;
});
console.log(arr2);//[3, 4, 5]

let arr3=arr.some(function(value){
    return value>2;
});
console.log(arr3);//true

let arr4=arr.every(function(value){
    return value>3;
});
console.log(arr4);//false

返回整數(shù)索引值，如果沒(méi)有匹配（嚴(yán)格匹配），返回-1. 匹配到返回 1。

var aa = [2, 5, 7, 3, 5];

console.log(aa.indexOf(5, "x")); // 1 ("x"被忽略)
console.log(aa.indexOf(5, "3")); // 4 (從3號(hào)位開(kāi)始搜索)
console.log(aa.indexOf(4)); // -1 (未找到)
console.log(aa.indexOf("5")); // -1 (未找到，因?yàn)? !== "5")

console.log(aa.lastIndexOf(5)); // 4
//console.log(aa.lastIndexOf(5, 3)); // 1 (從后往前，索引值小于3的開(kāi)始搜索)

//console.log(aa.lastIndexOf(4)); // -1 (未找到)

let ar3=[1,2,3,4,5];
let gh=ar3.reduce(function(last,now){
    return last*now;
},1)
console.log(gh);//120

相當(dāng)于reduce，只是reduceRight從右邊開(kāi)始計(jì)算

let ar33=[1,2,3,4,5];
let gh22=ar33.reduceRight(function(last,now){
    return last*now;
},1)
console.log(gh22);//120

判斷一個(gè)變量是否為數(shù)組,是返回true，不是返回false

let ss=22;
console.log(Array.isArray(ss));//false
console.log(Array.isArray(ar33));//true

ps：不兼容IE8.

let obj={
    x:1,
    y:2
}

let obj2=Object.create(obj,{z:{value:3}});
console.log(obj2);//Object {z: 3}
console.log(obj2.x);//1
//es6
let obj3={
    __proto__:obj,
    z:3
};
console.log(obj3);//Object {z: 3}

let objj={
    x:1,
    y:2
};
objj.k=4;
Object.defineProperty(objj,"j",{
    value:5,
    writable:false,//可寫(xiě)
    enumerable:false,//可便利
     configurable: true//可配置
});
objj.j=50;
objj.k=50;
console.log(objj);//Object {x: 1, y: 2, k: 50, j: 5}

let objj={
    x:1,
    y:2
};
Object.defineProperties(objj,{
    "m":{
        value:"mm",
    },
    "u":{
        value:"ll",
    }
})
console.log(objj);//Object {x: 1, y: 2, m: "mm", u: "ll"}

let sdf=Object.getOwnPropertyDescriptor(objj,"x");
console.log(sdf);//Object {value: 1, writable: true, enumerable: true, configurable: true}

console.log(Object.keys(obj));// ["x", "y"]

console.log(Object.getOwnPropertyNames(obj));

/*let aa={
    x:1,
    y:2
};
Object.preventExtensions(aa);
aa.fn=function(){

}
console.log(aa);//Object {x: 1, y: 2}*/

let aa={
    x:1,
    y:2
};
Object.seal(aa);
aa.fn=function(){

}
console.log(aa);//Object {x: 1, y: 4}

let aa={
    x:1,
    y:2
};
Object.freeze(aa);
aa.y=4;
console.log(aa);//Object {x: 1, y: 2}

console.log(Object.isExtensible(aa));//false 

console.log(Object.isSealed(aa));//true

console.log(Object.isFrozen(aa));//true

ps 以上方法均不兼容ie8

嚴(yán)格模式，重要其實(shí)就是es5中棄用了很多以前版本的語(yǔ)法，你再用就提示錯(cuò)誤。

使用var聲明變量嚴(yán)格模式中將不通過(guò)

何使用"eval"的操作都會(huì)被禁止

val作用域

ith被禁用

aller/callee 被禁用

禁止擴(kuò)展的對(duì)象添加新屬性會(huì)報(bào)錯(cuò)

除系統(tǒng)內(nèi)置的屬性會(huì)報(bào)錯(cuò)

delete使用var聲明的變量或掛在window上的變量報(bào)錯(cuò)

delete不可刪除屬性(isSealed或isFrozen)的對(duì)象時(shí)報(bào)錯(cuò)

對(duì)一個(gè)對(duì)象的只讀屬性進(jìn)行賦值將報(bào)錯(cuò)

對(duì)象有重名的屬性將報(bào)錯(cuò)

函數(shù)有重名的參數(shù)將報(bào)錯(cuò)

八進(jìn)制表示法被禁用

arguments嚴(yán)格定義為參數(shù)，不再與形參綁定

函數(shù)必須聲明在頂層

ES5里新增的關(guān)鍵字不能當(dāng)做變量標(biāo)示符使用，如implements, interface, let, package, private, protected, pulic, static, yield

call/apply的第一個(gè)參數(shù)直接傳入不包裝為對(duì)象

call/apply的第一個(gè)參數(shù)為null/undefined時(shí)，this為null/undefined

bind的第一個(gè)參數(shù)為null/undefined時(shí)，this為null/undefined