JavaScript中不为人知的数组方法介绍

var a = [1,2,3];
a.concat([4,5,6],7,8);//[1,2,3,4,5,6,7,8]

// 将 3 号位复制到 0 号位 
[1, 2, 3, 4, 5].copyWithin(0, 3, 4) 
// [4, 2, 3, 4, 5] 
// -2 相当于 3 号位， -1 相当于 4 号位 
[1, 2, 3, 4, 5].copyWithin(0, -2, -1) 
// [4, 2, 3, 4, 5] 
// 将 3 号位复制到 0 号位 
[].copyWithin.call({length: 5, 3: 1}, 0, 3) 
// {0: 1, 3: 1, length: 5} 
// 将 2 号位到数组结束，复制到 0 号位 
var i32a = new Int32Array([1, 2, 3, 4, 5]); 
i32a.copyWithin(0, 2); 
// Int32Array [3, 4, 5, 4, 5] 
// 对于没有部署 TypedArray 的 copyWithin 方法的平台 
// 需要采用下面的写法 
[].copyWithin.call(new Int32Array([1, 2, 3, 4, 5]), 0, 3, 4); 
// Int32Array [4, 2, 3, 4, 5]

var a = [1,2,3];
var en = a.entries();
en.next().value;//[0.1];

function isBigEnough(element, index, array) {
 return (element >= 10);
}
var passed = [12, 5, 8, 130, 44].every(isBigEnough);
// passed is false
passed = [12, 54, 18, 130, 44].every(isBigEnough);
// passed is true

[1, 2, 3].fill(4)   // [4, 4, 4]
[1, 2, 3].fill(4, 1)   // [1, 4, 4]
[1, 2, 3].fill(4, 1, 2)  // [1, 4, 3]
[1, 2, 3].fill(4, 1, 1)  // [1, 2, 3]
[1, 2, 3].fill(4, -3, -2) // [4, 2, 3]
[1, 2, 3].fill(4, NaN, NaN) // [1, 2, 3]
Array(3).fill(4);   // [4, 4, 4]
[].fill.call({length: 3}, 4) // {0: 4, 1: 4, 2: 4, length: 3}

function isBigEnough(value) {
 return value >= 10;
}
var filtered = [12, 5, 8, 130, 44].filter(isBigEnough);
// filtered is [12, 130, 44]

function isBigEnough(element) {
 return element >= 15;
}
[12, 5, 8, 130, 44].find(isBigEnough); // 130

function isBigEnough(element) {
 return element >= 15;
}
[12, 5, 8, 130, 44].findIndex(isBigEnough); // 3

let a = ['a', 'b', 'c'];
a.forEach(function(element) {
 console.log(element);
});
// a
// b
// c
//语法
array.forEach(callback(currentValue, index, array){
 //do something
}, this)
array.forEach(callback[, thisArg])

为数组中每个元素执行的函数，该函数接收三个参数：
currentValue(当前值)
数组中正在处理的当前元素。
index(索引)
数组中正在处理的当前元素的索引。
array
forEach()方法正在操作的数组。
thisArg可选
可选参数。当执行回调 函数时用作this的值(参考对象)

arr.includes(searchElement)
arr.includes(searchElement, fromIndex)

[1, 2, 3].includes(2);  // true
[1, 2, 3].includes(4);  // false
[1, 2, 3].includes(3, 3); // false
[1, 2, 3].includes(3, -1); // true
[1, 2, NaN].includes(NaN); // true

arr.indexOf(searchElement)
arr.indexOf(searchElement[, fromIndex = 0])

let a = [2, 9, 7, 8, 9]; 
a.indexOf(2); // 0 
a.indexOf(6); // -1
a.indexOf(7); // 2
a.indexOf(8); // 3
a.indexOf(9); // 1
if (a.indexOf(3) === -1) {
 // element doesn't exist in array
}

str = arr.join()
// 默认为 ","
str = arr.join("")
// 分隔符 === 空字符串 ""
str = arr.join(separator)
// 分隔符

let arr = ["a", "b", "c"];
let iterator = arr.keys();
// undefined
console.log(iterator);
// Array Iterator {}
console.log(iterator.next()); 
// Object {value: 0, done: false}
console.log(iterator.next()); 
// Object {value: 1, done: false}
console.log(iterator.next()); 
// Object {value: 2, done: false}
console.log(iterator.next()); 
// Object {value: undefined, done: true}

let array = arr.map(function callback(currentValue, index, array) { 
 // Return element for new_array 
}[, thisArg])
let numbers = [1, 5, 10, 15];
let doubles = numbers.map((x) => {
 return x * 2;
});
// doubles is now [2, 10, 20, 30]
// numbers is still [1, 5, 10, 15]
let numbers = [1, 4, 9];
let roots = numbers.map(Math.sqrt);
// roots is now [1, 2, 3]
// numbers is still [1, 4, 9]

var vegetables = ['parsnip', 'potato'];
var moreVegs = ['celery', 'beetroot'];
// 将第二个数组融合进第一个数组
// 相当于 vegetables.push('celery', 'beetroot');
Array.prototype.push.apply(vegetables, moreVegs);
console.log(vegetables); 
// ['parsnip', 'potato', 'celery', 'beetroot']

array.reduce(function(accumulator, currentValue, currentIndex, array), initialValue)
var total = [0, 1, 2, 3].reduce(function(sum, value) {
 return sum + value;
}, 0);
// total is 6
var flattened = [[0, 1], [2, 3], [4, 5]].reduce(function(a, b) {
 return a.concat(b);
}, []);
// flattened is [0, 1, 2, 3, 4, 5]

arr.slice();
//[0,end];
arr.slice(start);
//[start,end];
arr.slice(start,end);
//[start,end];

const isBiggerThan10 = (element, index, array) => {
 return element > 10;
}
[2, 5, 8, 1, 4].some(isBiggerThan10); 
// false
[12, 5, 8, 1, 4].some(isBiggerThan10); 
// true

var number = 1337;
var date = new Date();
var myArr = [number, date, "foo"];
var str = myArr.toLocaleString(); 
console.log(str); 
// 输出 "1,337,2017/8/13 下午8:32:24,foo"
// 假定运行在中文（zh-CN）环境，北京时区
var a=1234
a.toString()
//"1234"
a.toLocaleString()
//"1,234"
//当数字是四位及以上时，toLocaleString()会让数字三位三位一分隔，像我们有时候数字也会三位一个分号
var sd=new Date()
sd
//Wed Feb 15 2017 11:21:31 GMT+0800 (CST)
sd.toLocaleString()
//"2017/2/15 上午11:21:31"
sd.toString()
//"Wed Feb 15 2017 11:21:31 GMT+0800 (CST)"

array.splice(start)
array.splice(start, deleteCount) 
array.splice(start, deleteCount, item1, item2, ...)