ES6中Array对象的方法和扩展、string的扩展方法、数组的遍历
子车修平
目录
一、Array对象方法
1.Array.from()
将伪数组或可遍历对象转换为真正的数组（字符串，对象，类数组，set，map等）
let str = '1234';
const arr1 =Array.from(str);
console.log(arr1);//(4) ['1', '2', '3', '4']
const Arr = {
2:'a',
3:'b',
length:4,
}
console.log(Array.from(Arr));// (4) [undefined, undefined, 'a', 'b']2.array.find()
返回数组符合条件的第一个元素的值(数组与对象)
const arr = [1,2,3,4];//数组
let num = arr.find(item=>item==3);
console.log(num);//3
const arr1 = [ //对象
{realname:"张三1",age:18},
{realname:"张三2",age:17},
{realname:"张三3",age:19},
{realname:"张三4",age:17},
];
console.log(arr1.find(item=>item.age==17));//age: 17 realname: "张三2"3.array.findindex()
找出符合条件的成员的位置。
const arr = [1,2,3,4]; //数组
console.log(arr.findIndex(item=>item==4)); //3
const arrobj = [ //对象
{realname:"张三1",age:18},
{realname:"张三2",age:19},
{realname:"张三3",age:15},
{realname:"张三4",age:14},
]
console.log(arrobj.findIndex(item=>item.age==19)); //14.array.includes()
找出某个数组是否包含给定的值。
const arr = [1,2,3,4];
console.log(arr.includes(10));//有就返回true 没有就返回false二、Array扩展
1.array.map()
返回新数组
const arr = [1,2,3,4];
const newarr = arr.map(item=>item+2);
console.log(newarr); //从新输出一个数组，不是改变原的数组2. array.filter()
过滤
const arr = [1,2,3,4,5,6,7];
const newarr = arr.filter(item=> item%2==0);
console.log(newarr);3.array.reduce()
缩减
//total:即是初始值又是返回值
//currentValue:当前值
reduce第二个参数指定初始值
const arr = [1,2,3,4,5];
let sum = arr.reduce((total,currentValue)=>{
return total + currentValue;
},10) //可以指定初始值
console.log(sum);4.array.fill()
填充
let arr = [1,2,3,4,5,6,7];
arr.fill('x',1,3);
console.log(arr);//[1, 'x', 'x', 4, 5, 6, 7]三、string扩展
1.模板字符串的用法
function demo(){
return "end";
}
let es6 = "es6!";
let str = `hello,${es6},${demo()}`;
console.log(str);//hello,es6,end2.startsWith和endsWith用法
let str = "hello,es6!";
console.log(str.startsWith("hello"));//判断某个字符串前面是否包含hello 有就为true
console.log(str.endsWith("es6!"));//判断某个字符串后面是否包含es6 有就为true3.repeat字符串重复次数
console.log("hello".repeat(4));//hellohellohellohello四、数组的遍历
1.for of遍历数组的值
const arr = ["a","b","c","d"];
for(v of arr){
console.log(v); //a,b,c,d
}2.for in 遍历索引
const arr = ["a","b","c","d"];
for(let k in arr){
console.log(k); //0,1,2,3
}3.for of 遍历对象
const Person={realname:'zs',age:20}
const keys = Object.keys(Person);
for(let k of keys){
console.log(`k:${k}`,`v:${Person[k]}`)}; //k:realname v:zs k:age v:204.forEach的用法
let arr = [1,2,3,4];
arr.forEach((item,index)=>{
console.log(`v:${item},k:${index}`);
}) //v:1,k:0 v:2,k:1 v:3,k:2 v:4,k:3例题
1.找到一组同学中考试分数及格的第一个同学并输出到页面上
<ul class="score"></ul>
<hr>
<h1 class="username"></h1>
<script>
let person=[
{realname:'张三',score:'40'},
{realname:'李四',score:'40'},
{realname:'王五',score:'60'},
{realname:'赵六',score:'90'}
]
let str = '';
let userName='';
for(i=0;i<person.length;i++){
str = str + `<li>姓名：${person[i].realname},分数：${person[i].score}</li>`
}
document.querySelector('.score').innerHTML=str;
userName = person.find(item=>item.score>=60)
document.querySelector('.username').innerHTML=`姓名：${userName.realname},分数：${userName.score}`
</script>2.找出大于指定年龄（页面input框接收）的第一个人，并输出这个人的位置
<ul class="age"></ul>
<hr>
<input type="text" placeholder="请输入年龄" value="" class="mark">
<input type="button" value="查询" class="btn">
<h1></h1>
<script>
let person=[
{realname:'张三',age:'15'},
{realname:'李四',age:'18'},
{realname:'王五',age:'19'},
{realname:'赵六',age:'20'}
]
let str = '';
for(i=0;i<person.length;i++){
str = str + `<li>姓名：${person[i].realname},分数：${person[i].age}</li>`
}
document.querySelector('.age').innerHTML=str;
btn = document.querySelector('.btn')
btn.onclick=function(){
let num;
input=document.querySelector('.mark').value;//获得输入的值
num = person.findIndex(item=>item.age==input)//得到下标
if(num==-1){
document.querySelector('h1').innerHTML='查无此人';
}else{
num++;
document.querySelector('h1').innerHTML=`位置是${num}`
}
}
</script>3.输出一组人员信息，输出到页面信息如下（姓名，分数，是否及格60分）
const person=[
{realname:'zs1',age:20,score:50},
{realname:'zs2',age:20,score:70},
{realname:'zs3',age:20,score:80},
{realname:'zs4',age:20,score:90}
]
// 使用 for of 将内容显示在网页上
// let arr='';
// for(let v of person){
// arr =arr+ `<li>姓名：${v.realname},年龄：${v.age}</li>`
// }
// document.querySelector('ul').innerHTML=arr;
let mark='';
let newarr = person.filter(item=>{
let rer= item.score>60?'及格':'不及格'
mark+=`<li>姓名：${item.realname},年龄：${item.age},分数：${item.score},${rer}</li>`
})
document.querySelector('ul').innerHTML=mark;
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