函数和变量名

函数名和变量名相同时

  //如果函数名和变量名相同，函数会把变量作用域覆盖
   console.log(num)
        var num = 10;
        function num(){
            console.log("hellow word")
        }

  /*
        var num = function(){
            console.log("hellow word")
        }
        */
        console.log(num) //函数
        var num =10;
        function num(){
            console.log("hellow")
        }
        console.log(num);  //10

  function num(a){
            /*
            var a =function(){
                console.log("hellow word")
            }
            */
            console.log(a);     //function
            var a = 10;
            function a(){
                console.log("hellow word")
            }
            console.log(a); //10
        }
        num(20);

function关键字声明

 /*使用function关键字声明的函数，会将整段函数声明提前
        */
 console.log(go);
        go = 10;
        console.log(go);
        function go(){
            console.log("hellow word")

声明提前中函数名和变量名字相同的情况下

function num(a){
            console.log(a);
            var a =10;
            function a(){
                console.log("hellow")
            }
            console.log(a);
        }
        num(20);
        /*
        var a = 10;
        */

删除的方法

方法1

 var arr = [1,2,3]
        arr.pop();
        /*从后删除*/
        console.log(arr)

方法2 从前删除

 var arr = [2,3,4]
        arr.shift();
        console.log(arr)

方法3

  /*shift   pop*/
        var arr = [4,5,6,7,8]
        /*
        splice(index,howmany)
        index--从那个下标开始删除
        howmany删除几个
        */
        arr.splice(2,2)
        console.log(arr)

修改语句

/*
修改  "vue"
splice（index，howmany，value）
index 下标
howma 删除多少个
value 替代的值
*/
var arr = ["html","css","javascript"];
arr.splice(1,1,"vue")
console.log(arr)

includes的方法判断

var arr = [1,2,3,4,5,6,7,8,9];
console.log(arr.includes(6));
console.log(arr.includes(9));

                  /*splice 增加
          从下标的前面添加
          splice(index,0,value...)
          */
          var arr = [3,4,5,6]
          arr.splice(2,0,"html","css");
          console.log(arr)

增，删，改

   /*增，删，改，*/
        var arr = [3,4,5,6];
        /*
        [3,4,"html",5,6]
        splice(index,0,value)
        */
       arr.splice(2,0,"html");
       console.log(arr)
       /* 
       删除
       splice(index,howmany)
       */
      var test = [1,2,3,4,5]
      //[1,4,5]
      test.splice(1,2);
      console.log(test)

  var arr = [2,3,4,5]
        //[2,3,"vue",5]
        //arr.splice(index,howmany...value)
        arr.splice(2,1,"vue")
        console.log(arr)

查询

  /*
        indexOf
        -1
        */
    //    var arr = [2,3,4];
    //    console.log(arr.indexOf(2));
    //    console.log(arr.indexOf(8));
    var arr = [2,3,4,5,6];
    var test = arr.slice(1,3);
    //slice(startIndex,endIndex)  tips：不包含结束的下标
    console.log(test)

 var arr = [1,2,3,4,5,8];
        var sum = 0;
        for(var i=0;i<arr.length;i++){
            sum +=arr[i];
        }
        console.log(sum)

练习

  var arr =[
            {name:"李四",age:"18岁"},
            {name:"高四",age:"20岁"},
            {name:"樟四",age:"8岁"},
            {name:"李四",age:"16岁"},
        ]
       var test = [];
       for(var i=0;i<arr.length;i++){
           //console.log(arr[i].age)
           var age = parseInt(arr[i].age);
           console.log(age)
           if(age>16){
               console.log(arr[i])
               test.push(arr[i])
           }
       }
       console.log(test)

 var arr = [1,2,3,4,5,6,7,8,9]
        //[[1,2,3],[4,6,7],[7,8,9]]
        // var newArr = [];
        // var len = arr.length;
        // for(let i =0,j =0; i<len; i+=9,j++){
        //     newArr[j] = arr.splice(0,8);
        // }
        // console.log(newArr)
        /*slice(0,3)  0-2
        slice(3,6)     3-5
        slice(6,0)      6-8
        */
       var test = [];
            for(var i=0;i<arr.length;i+=3){
                //console.log(i)
                test.push(arr.slice(i,i+3))
            }
            console.log(test)

求最小值

 var arr = [4,6,18,1];
      //alert(Math.min.apply(null,arr))
      //console.log(Math.min.apply(null,arr))
      /*假设  var min = arr[0]*/
      var min =arr [0];
      for(var i=1;i<arr.length;i++){
          if(min>arr[i]){
              min =arr[i];
          }
      }
      console.log(min)

示例

 var arr = [
        {name:"lisi",age:"12px"},
        {name:"wangwn",age:"13px"},
        {name:"zhangsan",age:"14px"},
        ]
        for(var i=0;i<arr.length;i++){
        // var age = parseInt(arr[i].age);
        // console.log(age)
            var age = parseInt(arr[i].age)*2
            //console.log(age)
            arr[i].age = age;
            arr[i].like = true;
            if(arr[i].age>24){
                arr[i].like = true;
            }else{
                arr[i].like= false
            }
        }
        console.log(arr)

 // var str = "你武汉";
        // console.log(str.includes("武"))
        var searchs  =[
            {
                spell:"A",
                citys:[
                    {name:"阿里",id:1001},
                    {name:"阿拉",id:1001},
                    {name:"阿克",id:1001}
                ]
            },{
                spell:"T",
                citys:[
                    {name:"天下",id:2001},
                    {name:"天天",id:2002},
                    {name:"天里",id:2003}
                ]
            }
        ]
        //var keyword = "里";
        var arr = [];
        var input = document.getElementById("input");
        //获取关键字
        input.onkeydown = function(event){
            if(event.keyCode ==13){
              if(this.value !=""){
                  var kw = this.value.trim();
                  //使用关键字对数组进行遍历
                  for (var i=0;i<searchs.length;i++){
                      var citys = searchs[i].citys;
                      for ( var j = 0;j < citys.length;j++){
                        if (citys[j].name.includes(kw)){
                            arr.push(citys[j]);
                        }
                      }
                  }
                  console.log(arr)
              }
            }
        }

trim去除字符串前后尾的空格

 var str = "   fdsf     "
        console.log(str.trim())