25array4.html
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Document</title>
</head>
<body>
<script>
// forEach()
var arr = [11,3,56,56,34,100,9,100];
/*
arr.forEach(function(item,index) {
console.log(index+"-"+item);
});
*/
arr.forEach((item,index)=>{
//console.log(index+"-"+item);
if(item%2===0) {
console.log(item);
}
});
// 求上述数组最大值
var max = arr[0];
arr.forEach((item)=>{
if(item>max) {
max = item;
}
});
console.log(max);
// indexOf() 查找元素在数组中第一次出现的索引 假如不存在返回值-1
var index = arr.indexOf(200);
var index2 = arr.lastIndexOf(100); //从右往左找
console.log(index);//4
console.log(index2); // 6
// 对数组进行去重
function noRepeat(arr) {
var newArr = [];
// 对arr循环 每一次拿到元素 判断是否在newArr中 没有就加到newArr
arr.forEach((item)=>{
if(newArr.indexOf(item) === -1) {
newArr.push(item);
}
});
return newArr;
}
console.log(noRepeat(arr));
// map filter reduce some every 不会改变原数组
var array = [12,14,5,6,32,10];
/*var newArr = array.map((item)=>{
return item*1.2;
});
// filter过滤 由函数返回值为true的元素所组成
var newArr = array.filter((item)=>{
return item>12;
});
*/
// reduce 收敛
/*
第一次 prev 12 next 14
第二次 prev undefined next 5
第三次 prev undefined next 6
...
从第二次开始的prev 是上一次的函数返回值
*/
var sum = array.reduce((prev,next)=>{
console.log(prev+"---"+next);
return prev+next;
});
// 当reduce传入第二个参数 第一次的prev指向第二个参数
var sum2 = array.reduce((prev,next)=>{
console.log(prev+"---"+next);
return prev+next;
},6);
console.log(sum2);
//console.log(newArr,array);
// some 返回true/false
var arr2 = [10,4,5,6,11,20]; //
var res = arr2.some((item)=>{
console.log(item);
return item>100;
});
console.log(res); // true
console.log("--------------");
// every 直到第一个为false停止循环 否则返回true
var res2 = arr2.every((item)=>{
console.log(item);
return item>10;
});
console.log(res2);
</script>
</body>
</html>
26array5.html
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Document</title>
</head>
<body>
<script>
// Math.pow()
// es6新增的 from 把数组或类数组变成数组 会复制一份
var arr = [1,2,3];
var newArr = Array.from(arr);
console.log(newArr);
// 类数组 并不是真正的数组 而是对象 arguments
function fn() {
//arguments.push(10); 报错
var arguments = Array.from(arguments);
arguments.push(12);
console.log(arguments instanceof Array);
}
fn(1,2,3);
//console.log(arr instanceof Array);
var obj = {
"0": 10,
"1":20,
length: 2
}
var arr2 = Array.from(obj);
console.log(arr2);
// of fill copyWithin
var array = new Array(3); // var array = [3];
var array1 = new Array(3,4);
var array2 = Array.of(3,4);// 3是元素
console.log(array,array.length);
console.log(array1,array1.length);
console.log(array2,array2.length);
// fill copyWithin
var res = [1,2,3,4].fill(5,1,3); // [1,5,5,4]
var res2 = [1,2,3,4].copyWithin(1,0,2); // 用序号为0的元素一直到序号为2但不包含2的元素 1 2
console.log(res);
console.log(res2);// [1,1,2,4]
// es7 includes
console.log([10,12,23,43].includes(100));// false 不存在 true存在
// find findIndex （keys values）
var find = [1,2,3,4,5,3].find((item,index,arr)=>{
console.log("fn");
return item==13;
});
var findIndex = [1,2,3,4,5,3].findIndex((item,index,arr)=>{
return item==3;
});
console.log(findIndex);
</script>
</body>
</html>
27array6.html
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="X-UA-Compatible" content="ie=edge">
<title>Document</title>
</head>
<body>
<script>
// 解构赋值 解析数组或对象的结构为不同的变量提取值
//var name = "along";
//var age = 32;
var [name,age] = ["along",32];
console.log(name);
console.log(age);
//var [x,y,z] = [1,[2.2,2.3]];
//var [x,[y,z]] = [1,[2.2,2.3]];
//console.log(x,y,z); // 1 [2.2,2.3] undefined
var [json,arr,num] = [{a:10,b:20},[1,2,3],10];
var [,,x=4] = [1,2];
console.log(x);
var [x,...y] = [10,20,30,40];// 剩余项
console.log(x,y);// 10 [20,30,40]
var arr = [1,2,3];
var [...arr1] = arr; // 克隆数组
console.log(arr1);
var x = 10, y = 20;
/*
var temp = x;
x = y;
y = temp;
*/
[x,y] = [y,x];
console.log(x,y);
</script>
</body>
</html>
原文地址：https://www.cnblogs.com/HiJackykun/p/11135520.html
时间： 2024-09-29 21:36:26