1. toString()

JavaScript 方法 toString() 把數(shù)組轉(zhuǎn)換為數(shù)組值（逗號分隔）的字符串莺匠。

var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.toString();  // "Banana,Orange,Apple,Mango"

2. join()

將所有數(shù)組元素結(jié)合為一個字符串。
可以規(guī)定分隔符

var fruits = ["Banana", "Orange","Apple", "Mango"];
fruits.join(" --- ");   // "Banana --- Orange --- Apple --- Mango"

3. concat()

合并數(shù)組

var arr1 = ["Cecilie", "Lone"];
var arr2 = ["Emil", "Tobias", "Linus"];
var myChildren = arr1.concat(arr2,  ["Robin", "Morgan"]);   // ["Cecilie", "Lone", "Emil", "Tobias", "Linus", "Robin", "Morgan"]

4. pop()

從數(shù)組中刪除最后一個元素：(改變原數(shù)組)

var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.pop();  // "Mango"
fruits  // ["Banana", "Orange", "Apple"]

5. push()

在數(shù)組結(jié)尾處 向數(shù)組添加一個新的元素：(改變原數(shù)組)

var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.push("Kiwi");   // 5 新數(shù)組的length
fruits  // ["Banana", "Orange", "Apple", "Mango", "Kiwi"]

6. shift()

刪除數(shù)組首個元素

var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.shift();  // "Banana"
fruits  // ["Orange", "Apple", "Mango"]

7. unshift()

向數(shù)組開頭添加新元素

var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.unshift("Lemon");    // 向 fruits 添加新元素 "Lemon"
fruits  // ["Lemon", "Banana", "Orange", "Apple", "Mango"]

8. slice()

用數(shù)組的某個片段切出新數(shù)組十兢。(原數(shù)組不變)

var fruits = ["Banana", "Orange", "Lemon", "Apple", "Mango"];
var citrus = fruits.slice(1, 3); 

9. splice()

向數(shù)組添加新項：

var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.splice(2, 1, "Lemon", "Kiwi");  // ["Apple"]
fruits // ["Banana", "Orange", "Lemon", "Kiwi", "Mango"]

第一個參數(shù)（2）定義了應(yīng)添加新元素的位置（拼接）趣竣。
第二個參數(shù)（0）定義應(yīng)刪除多少元素。
其余參數(shù)（“Lemon”旱物，“Kiwi”）定義要添加的新元素遥缕。
splice() 方法返回一個包含已刪除項的數(shù)組：


var fruits = ["Banana", "Orange", "Apple", "Mango"];
fruits.splice(0, 1);   // ["Banana"]
fruits  // ["Orange", "Apple", "Mango"]
第一個參數(shù)（0）定義新元素應(yīng)該被添加（接入）的位置。
第二個參數(shù)（1）定義應(yīng)該刪除多個元素宵呛。
其余參數(shù)被省略单匣。沒有新元素將被添加。

10. reverse()

11. reduce

迭代數(shù)組的所有項，累加器户秤，數(shù)組中的每個值（從左到右）合并码秉，最終計算為一個值

let arr = [{done: true,name: '11'},{done: true,name: '22'},{done: false,name: '33'},{done: true,name: '44'}]
var sum = arr.reduce((it) => {return it.done})
var sum = arr.reduce((pre, current) => {return pre+(current.done ? 1 : 0)}, 0)

sum  // 3

delete 運算符

delete 刪除之后位置還在內(nèi)容是undefined,length 不變
var fruits = ["Banana", "Orange", "Apple", "Mango"];
delete fruits[0]; // 把 fruits 中的首個元素改為 undefined

數(shù)組的方法面試很容易被問到. reduce sort