前端js常用方法和事件

1.form表单触发submit事件去掉值为''和null的数据

function () {
  var formData = $('#search').serializeArray()
  var data = {}
  formData.map((item, index) => {
    if (item.value == 'null' || item.value == '') return
    data[item.name] = item.value
  })

2.递归渲染数据列表

recursionOutline($('元素接点'),'数据'）
function recursionOutline(el, data) {
  el.empty()//先清空
  for (var i = 0; i < data.length; i++) {
    const element = data[i];
    if (element.childNode) {//包含子节点，这里的childNode是我的子节点属性
      el.append(`
 ${element.doc_number + "." + element.doc_title}
`);
      recursionOutline(el.children("li").last().children("ul"), element.childNode);//递归渲染子节点
    } else {//不包含子节点
      el.append(`
${element.doc_number + "." + element.doc_title}
`)
    }
  }
};

3.数据类型转换

1）将数组转换成对象

var arr= ['1', '2', '3', '4', '5', '6', '7', '8'];
var obj= {...arr}
console.log(obj); // {'0': '1','1': '2', '2': '3','3': '4','4': '5','5': '6','6': '7','7': '8'}

2）将数组转换成字符串

var arr= ['1', '2', '3', '4', '5', '6', '7', '8'];
var str= arr.join('')
console.log(str); // 12345678

4.判断两个数组中的相同值

var arr1= ['1', '2', '3', '4', '5', '6', '7', '8'];
var arr2= ['1', '2', '3'];
var array= [...new Set(arr1)].filter(item => arr2.includes(item));
console.log(array); // [ '1', '2', '3' ]

5.reduce的高级用法

var arr1= ['1', '2', '3', '4', '5', '6', '7', '8'];
var arr2= ['1', '2', '3'];
var array= [...new Set(arr1)].filter(item => arr2.includes(item));
console.log(array); // [ '1', '2', '3' ]

1）计算数组中每个元素出现的次数

let arr = ['a', 'c', 'd', 'b','a'];

let objnum = arr.reduce((pre,cur)=>{
  if(cur in pre){
    pre[cur]++
  }else{
    pre[cur] = 1 
  }
  return pre
},{})
console.log(objnum); //{a: 2, c: 1, d: 1, b: 1}

2）数组去重

let arr = [1,2,3,4,4,1]
let newArr = arr.reduce((pre,cur)=>{
    if(!pre.includes(cur)){
      return pre.concat(cur)
    }else{
      return pre
    }
},[])
console.log(newArr);// [1, 2, 3, 4]

3）将单层嵌套数组合并

let arr = [[0, 1], [2, 3], [4, 5]]
let newArr = arr.reduce((pre,cur)=>{
    return pre.concat(cur)
},[])
console.log(newArr); // [0, 1, 2, 3, 4, 5]

4）将多层嵌套数组转化为一维

let arr = [[0, 1], [2, 3], [4,[5,6,7]]]
const newArr = function(arr){
   return arr.reduce(
        (pre,cur)=>pre.concat(
        Array.isArray(cur)?newArr(cur):cur
        ),[])
}
console.log(newArr(arr)); //[0, 1, 2, 3, 4, 5, 6, 7]

5）对象数组求和

var result = [
    {
        subject: 'math',
        score: 10
    },
    {
        subject: 'chinese',
        score: 20
    },
    {
        subject: 'english',
        score: 30
    }
];

var sum = result.reduce(function(prev, cur) {
    return cur.score + prev;
}, 0);
console.log(sum) //60