数组的遍历

## 数组使用

> 数组合并

ES5的写法

```

let arr1=[0,1,2];

let arr2=[3,4,5];

Array.prototype.push.apply(arr1,arr2);

```

ES6的写法

```

let arr3=['a','b','c'];

let arr4=[3,4,5];

arr3.push(...arr4);

```

> 几个属性的理解

- Object.keys(obj) :返回对象自身的所有可枚举的属性的键名

```

let arr1keys = Object.keys(arr1);  // ["0", "1", "2", "3", "4", "5"]

let arr3keys = Object.keys(arr3);  // ["0", "1", "2", "3", "4", "5"]

```

- Object.getOwnPropertyNames(obj):返回一个数组，包含对象自身的所有属性

```

let temp1 = Object.getOwnPropertyNames(arr1);// ["0", "1", "2", "3", "4", "5", "length"]

```

- Object.getOwnPropertySymbols(obj):返回一个数组，包含对象自身的所有Symbol属性

```

let temp2 = Object.getOwnPropertySymbols(arr2);// []

```

> for...of  、for...in 和 forEach

- for of是遍历键值

```

for( let i of arr3 ){

console.log(i);// a b c 3 4 5

}

```

- for...in循环：只遍历对象自身的和继承的可枚举的属性、for in是遍历键名

```

for( let i in arr3 ){

console.log(i);// 0 1 2 3 4 5

}

```

- forEach循环

```

arr3.forEach(function(item,index){

console.log(item);// a b c 3 4 5

console.log(index);// 0 1 2 3 4 5

});

```

> 数组过滤

- 扩展数组`prototype`属性过滤数组

```

let arrayAll = [{'id':'111','name':'aaa'},

{'id':'222','name':'bbb'},

{'id':'333','name':'ccc'}];

let arrayDel = [{'id':'111','name':'aaa'}];

Array.prototype.indexOf = function(val) {

for (var i = 0; i < this.length; i++) {

if (val.id == this[i].id) return i;

}

return -1;

};

Array.prototype.remove = function(val) {

var index = this.indexOf(val);

if (index > -1) {

this.splice(index, 1);

}

};

for (let i of arrayDel.length) {

let obj = arrayDel[i];

array.remove(obj);

}

console.dir(array);

```

- lodash 库 `differenceBy` 方法

```

let newArray = differenceBy(array,[{'id':'111','name':'aaa'}],'id');

console.dir(newArray);

```

> ES 6 常用 `API`