JS数组Array常用方法汇总+实例

var arr1 = new Array(); //创建一个空数组
var arr2 = new Array(15); // 创建一个长度为15的数组
var a = new Array([15]); //指创建一个数组，长度为1，并且第一位是15
var arr3 = new Array("sf","zs","zsf"); // 创建一个包含3个字符串的数组

var arr4 = []; //创建一个空数组
var arr5 = [15]; // 创建一个数组，长度为1，包含‘15'数字
var arr6 = ["sf","zs","zsf"]; // 创建一个包含3个字符串的数组

ar arr = [1,2,3];
console.log(arr.pop());     //3
console.log(arr);           //[1,2]---原数组改变

var arr = [1,2,3]
console.log(arr.shift());       //1
console.log(arr);               //[2,3]---原数组改变

var arr = [1,2,3];
console.log(arr.push("hello"));  //4
console.log(arr);                //[1,2,3,"hello"]---原数组改变
console.log(arr.push("a","b"));  //6
console.log(arr);                //[1,2,3,"hello","a","b"]---原数组改变

var arr = [1,2,3];
console.log(arr.unshift("hello"));  //4
console.log(arr);                   //["hello",1,2,3]---原数组改变
console.log(arr.unshift("a","b"));  //6
console.log(arr);                   //["a","b","hello",1,2,3]---原数组改变

var arr = [6,1,5,2,3];
console.log(arr.sort());    //[1, 2, 3, 5, 6]
console.log(arr);           //[1, 2, 3, 5, 6]---原数组改变

// 案例一：看上去正常的结果
['Google', 'Apple', 'Microsoft'].sort(); // ['Apple', 'Google', 'Microsoft'];

// 案例二：apple排在了最后
['Google', 'apple', 'Microsoft'].sort(); // ['Google', 'Microsoft", 'apple']

// 案例三：无法理解的结果
[10, 20, 1, 2].sort(); // [1, 10, 2, 20]

var arr = [10, 20, 1, 2];
arr.sort((x, y)=> {
	if (x < y) {
		return -1;
	}
	if (x > y) {
		return 1;
	}
	return 0;
});
console.log(arr); // [1, 2, 10, 20]

var arr = [13, 24, 51, 3];
console.log(arr.reverse()); //[3, 51, 24, 13]
console.log(arr); //[3, 51, 24, 13](原数组改变)

array.splice(index, howmany, item1, ....., itemX)

var arr = [1,3,5,7,9,11];
var arrRemoved = arr.splice(0,2);
console.log(arr); //[5, 7, 9, 11]
console.log(arrRemoved); //[1, 3]
var arrRemoved2 = arr.splice(2,0,4,6);
console.log(arr); // [5, 7, 4, 6, 9, 11]
console.log(arrRemoved2); // []
var arrRemoved3 = arr.splice(1,1,2,4);
console.log(arr); // [5, 2, 4, 4, 6, 9, 11]
console.log(arrRemoved3); //[7]

var arr = [1,2,3];
console.log(arr.join());         //1,2,3
console.log(arr.join("-"));      //1-2-3

function repeatString(str, n) {
	return new Array(n + 1).join(str);
}
console.log(repeatString("abc", 3)); // abcabcabc
console.log(repeatString("Hi", 5)); // HiHiHiHiHi

const arr1 = [1,2,3];
const arr2 = [4,5,6];
const arr3 = arr1.concat(arr2);
console.log(arr3);  //[1,2,3,4,5,6]

var arr = [1,3,5,7,9,11];
var arrCopy1 = arr.slice(1);
var arrCopy2 = arr.slice(1,4);
var arrCopy3 = arr.slice(1,-2);
var arrCopy4 = arr.slice(-4,-1);
console.log(arr); //[1, 3, 5, 7, 9, 11](原数组没变)
console.log(arrCopy1); //[3, 5, 7, 9, 11]
console.log(arrCopy2); //[3, 5, 7]
console.log(arrCopy3); //[3, 5, 7]
console.log(arrCopy4); //[5, 7, 9]

var arr = [1,2,3];
console.log(arr.toString());     //1,2,3
console.log(arr);                //[1,2,3]---原数组未改变

var arr = [1,2,3];
console.log(arr.valueOf());         //[1,2,3]
console.log(arr);                   //[1,2,3]
//为了证明返回的是数组自身
console.log(arr.valueOf() == arr);  //true

var arr = ["h","e","l","l","o"];
console.log(arr.indexOf("l"));        //2
console.log(arr.indexOf("l",3));      //3
console.log(arr.indexOf("l",4));      //-1
console.log(arr.indexOf("l",-1));     //-1
console.log(arr.indexOf("l",-3));     //2

var arr = ["h","e","l","l","o"];
console.log(arr.lastIndexOf("l"));        //3
console.log(arr.lastIndexOf("l",3));      //3
console.log(arr.lastIndexOf("l",1));      //-1
console.log(arr.lastIndexOf("l",-3));     //2
console.log(arr.lastIndexOf("l",-4));     //-1

var arr = [1, 2, 3, 4, 5];
arr.forEach((item, index, a)=>{
	console.log(item + '|' + index + '|' + (a === arr));
});
// 输出为：
// 1|0|true
// 2|1|true
// 3|2|true
// 4|3|true
// 5|4|true

 let arr = [10, 30, 50, 60, 120, 230, 340, 450]
 let newArr = arr.map(item => {
     return item * 2
 })
 console.log(newArr); //[20, 60, 100, 120, 240, 460, 680, 900]
 console.log(arr); //[10, 30, 50, 60, 120, 230, 340, 450]

//过滤出索引为3的倍数 或者 值大于8的元素
var arr = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
var arr2 = arr.filter((item, index) => { 
	return index % 3 === 0 || item >= 8; 
}); 
console.log(arr2); //[1, 4, 7, 8, 9, 10]

var arr = [1, 2, 3, 4, 5];
var arr2 = arr.every((x)=> {
	return x < 10;
}); 
console.log(arr2); //true
var arr3 = arr.every((x) => {
	return x < 3;
}); 
console.log(arr3); // false

var arr = [1, 2, 3, 4, 5];
var arr2 = arr.some((x)=> {
	return x < 3;
}); 
console.log(arr2); //true
var arr3 = arr.some((x)=> {
	return x < 1;
}); 
console.log(arr3); // false

 // 作用:对数组中所有的内容进行汇总   要传至少两个值
 let arr = [10, 30, 50, 60, 120, 230, 340, 450]
 let newArr = arr.reduce((pre, n) => {
     return pre + n
 }, 0)
 console.log(newArr);

var arr = [1,2,3,4,5];
var sum = arr.reduceRight(function(pre, cur, index, array){
	return pre + cur;
},10);
console.log(sum); //25

let arr = [10, 2, 9, 17, 22];
let index = arr.findIndex((item) => item > 13)
console.log(index);  // 3

var arr = [6,1,5,2,3];
console.log(arr.sort());    //[1, 2, 3, 5, 6]

var arr = [6,1,5,2,3];
console.log(arr.sort((a,b)=>{return b - a}));//[6,5,4,3,2,1]

var arr = [6,1,5,2,3];
console.log(arr.sort().reverse());    //[6,5,4,3,2,1]

function uniqueArray(arr) {
	var temp = [];
	for (var i = 0; i < arr.length; i++) {
		if (temp.indexOf(arr[i]) == -1) {
			temp.push(arr[i]);
		}
	}
	return temp;
}

var r = [],
arr = ['apple', 'strawberry', 'banana', 'pear', 'apple', 'orange', 'orange', 'strawberry'];
r = arr.filter(function (element, index, self) {
  return self.indexOf(element) === index;
});
consolo.log(r)//['apple', 'strawberry', 'banana', 'pear', 'orange']

//数组重名去重
var resources = [
  { name: "张三", age: "18" },
  { name: "张三", age: "19" },
  { name: "张三", age: "20" },
  { name: "李四", age: "19" },
  { name: "王五", age: "20" },
  { name: "赵六", age: "21" }
]
var temp = {};
resources = resources.reduce((prev, curv) => {
  if (!temp[curv.name]) {// 如果临时对象没有就把这个名字加进去，同时把当前的这个对象加入到prev中
  	temp[curv.name] = true;
    prev.push(curv);
  }
	return prev
}, []);
console.log(resources);
//[
//  { name: "张三", age: "18" },
//  { name: "李四", age: "19" },
//  { name: "王五", age: "20" },
//  { name: "赵六", age: "21" }
//]

var arr = [1,1,1,2,2,2,2,2,2,2,3,3,3,4,4,5,6,7,7,8];
var maxNum = 0;
var maxName = "";
var obj = {};
arr.forEach((ele,index)=>{
	obj[ele] ? obj[ele] += 1 : obj[ele] = 1;
})
for(let r in obj) {
	if(obj[r]>maxNum){
		maxNum = obj[r]
		maxName = r
	}
}

console.log(`最多重复的数${maxName},重复次数为:${maxNum}`) //最多重复的数2,重复次数为:7