数组（Array）方法

// 合并数组
var hege = ["Cecilie", "Lone"];
var stale = ["Emil", "Tobias", "Linus"];
var kai = ["Robin"];
var children = hege.concat(stale,kai);
console.log(children);//["Cecilie", "Lone","Emil", "Tobias", "Linus","Robin"] 
// 索引查找数组
var arr=[1,2,3,4];
console.log(arr.slice(0,3));//1,2,3
// 数组改字符串
var arr=[1,2,3];
console.log(arr.join());//1,2,3
// 排序
var arr=[1,5,2,4,5];
console.log(arr.sort());//[1,2,4,5,5]
// 倒序
var arr=[1,2,3,4,5];
console.log(arr.reverse());//[5,4,3,2,1]
数组中更换元素的位置
var arr=[1,2,3,4,5];
console.log(arr.copyWithin(1,0,2))//[11245]
console.log(arr.copyWithin(2,0,3))//[12123]
返回可迭代对象
var fruits = ["Banana", "Orange", "Apple", "Mango"];
var x=fruits.entries();
var a=x.next().value;
var b=x.next().value;
var c=x.next().value;
var d=x.next().value;
var arr=[];
arr.push(a,b,c,d);
console.log(arr);
//every 检测数组所有元素是否都符合指定条件
var arr=[51,42,54,85,21,21,15,16,15];
console.log(arr.every(a));
function a(age){
return age>18
}
//fill 使用固定值填充数组
var arr=[1,2,3,4,5];
console.log(arr.fill("a"));//["a","a","a","a","a"]
console.log(arr.fill("n",1,3))//[1,"n","n",4,5]
console.log(arr.fill(8,0,5))//[8,8,8,8,8]
console.log(arr.fill(5,1,3))//[1,5,5,4,5]
//filter 过滤
var arr=[1,2,3,4,5,6,7];
console.log(arr.filter(function(data){
return data>5;
}))
[6,7]
//find 查找第一次返回值
var arr=[1,2,3,4,5,6,7];
console.log(arr.find(function(data){
return data>5;
}))
//6
//findIndex 查找第一次返回值索引
var arr=[1,2,3,4,5,6,7];
console.log(arr.findIndex(function(data){
return data>5;
}))
//5
//forEach 调用数组的每个元素，并将元素传递给回调函数
var arr=[1,2,3,4,5,6];
console.log(arr.forEach(function(item,index){
console.log(index,item);
})) //0 1
// 1 2
// 2 3
// 3 4
// 4 5
// 5 6
// from 字符串转数组
var myArr = Array.from("1234");
console.log(myArr);//1,2,3,4
var myArr = Array.from("1234",x=>x*10);
console.log(myArr);//10,20,30,40
//includes 判断数组内是否包含指定的值
console.log([12,23,45,65,54].includes(23,45));//false
console.log([12,23,45,65,54].includes(23,1));//true
console.log([12,23,45,65,54].includes(23,));//true
//indexOf 返回数组中指定值的索引
console.log([1,2,3,4,5,6].indexOf(5));//4
console.log([1,2,3,4,5,6].indexOf(5,5));//-1
//isArray 判断对象是否是数组
console.log(Array.isArray([1,2,3,4,5]));//true
//join 数组转字符串
console.log([1,2,3,4,5].join("|"));//1|2|3|4|5
console.log([1,2,3,4,5].join());//12345
//keys 数组转可迭代对象
var arr=[1,2,3]
var s=arr.keys();
var z=s.next().value;
var x=s.next().value;
var c=s.next().value;
arr.push(z,x,c);
console.log(arr);
//map 映射
var arr=[1,2,3,4,5];
console.log(arr.map(function(item,index){
return item*10
}))
//pop 数组结尾删除
var arr=[1,2,5,4];
console.log(arr.pop());//4
//push 数组结尾添加
var arr=[1,2,3,4];
console.log(arr.push(5));//5
//reduce 数组累加计算一个值
var arr=[1,2,3,4,5,6,7,8,9,10];
console.log(arr.reduce(function(init,item){
// console.log(init);
return init+item;
},0))//55
//reduceRight 数组累加计算一个值
var arr=[1,2,3,4,5,6,7,8,9,10];
console.log(arr.reduceRight(function(init,item){
// console.log(init);
return init+item;
},0))//55
//reverse 倒序
console.log([1,2,3,4,5].reverse());//[5,4,3,2,1]
//shift 删除第一个
console.log([1,2,3,4].shift());//1
// slice 选取数组一部分
console.log([1,2,3,4,5].slice(1,3));//[2,3]
//some 监测数组中是否符合条件
console.log([1,2,3,4].some(function(item,index,arr){
return item>4;
}))//false
// sort 排序
console.log([2,1,5,4,5].sort());//[1,2,4,5,5]
//splice 增删改查
var arr=[1,2,3];
arr.splice(2,0,"5");
console.log(arr);//[1,2,"5",3]
//tostring 数组转字符串
console.log([1,2,3,4].toString());//"1,2,3,4"
//unshift 开头添加元素
console.log([1,2,1,2].unshift(5));//5
//valueOf() 查看数组的元素
console.log([1,2,1,2].valueOf());//[1, 2, 1, 2]
console.log([1,2,1,2]);//[1, 2, 1, 2]