1.數(shù)據(jù)類型的轉(zhuǎn)換

boolean,string-->number
強(qiáng)制轉(zhuǎn)換Numbe()
Number() -->只能識(shí)別純數(shù)字的字符串恩沽，只要帶了英文的字符串孕索，都輸出NaN
"20px" -->NaN
NaN -->不是一個(gè)數(shù)字

    <script>
        var a = true;
        var b = false;
        var c = "20";
        var d ="20px";
        var e = "good"
        console.log(Number(a));
        console.log(Number(b));
        console.log(Number(c));
        console.log(Number(d));
        console.log(Number(e));
    </script>

數(shù)據(jù)類型轉(zhuǎn)換.png

2.自動(dòng)轉(zhuǎn)換

    <script>
        /*
        自動(dòng)轉(zhuǎn)換(隱式轉(zhuǎn)換)
        在算術(shù)計(jì)算中的自動(dòng)轉(zhuǎn)換: 先將數(shù)據(jù)轉(zhuǎn)為number嘿辟，再進(jìn)行計(jì)算
        +垂谢，-氨菇，*假哎，/，%
        */
       var a = 20;
       var b = true;
       var c = a-b;
       // var c = a - Number(b);
       console.log(c);
       /* 特殊+
        只要一邊為字符串歉嗓，那么+起到拼接符的作用丰介，結(jié)果為字符串
        */
       var d = "20";
       var e = 1;
       console.log(d+e);
    </script>

自動(dòng)轉(zhuǎn)換.png

    <script>
        /*
        比較運(yùn)算中的自動(dòng)轉(zhuǎn)換:
        先將數(shù)據(jù)轉(zhuǎn)為number，再比較，結(jié)果返回boolean值
        <,>,==,!=,<=,>=
        */
       var a = "20";
       var b = true;
       console.log(a>b);
       // console.log(Number(a)>Number(b));
    </script>

比較運(yùn)算中的自動(dòng)轉(zhuǎn)換.png

3.parseInt(),parseFloat()

    <script>
        /*
        string--number
        parseInt()
        parseFloat();
        被轉(zhuǎn)換的字符串第一位必須為數(shù)字
        */
       var a = "12.343px";
       var e = "a12.px"
       var b = parseInt(a);
       var c = parseFloat(a);
       console.log(b);
       console.log(c);
       console.log(parseInt(e));
    </script>

parse.png

4.強(qiáng)制轉(zhuǎn)換

    <script>
        /*
        1.強(qiáng)制轉(zhuǎn)換
        number,string,boolean
        */
       /*
       其他-->number
       Number()
       string--number
       parseInt()
       parseFloat()
       */
      /*
      其他-->boolean
      Boolean()
      只有5種情況為false
      0哮幢，"",NaN,null,undefined
      */
     var a = "hello world";
     var c = 1;
     var b = Boolean(a);
     console.log(b);
     console.log(Boolean(""));
     /*
     其他-->string
     String()
     toString()
     */
    var e = 20;
    var f = String(e);
    var g = e.toString();
    console.log(typeof f);
    console.log(typeof g);
    </script>

強(qiáng)制轉(zhuǎn)換.png

5.算術(shù)带膀，比較，邏輯運(yùn)算

    <script>
        /*
        發(fā)生在運(yùn)算中
        算術(shù)運(yùn)算+橙垢，-垛叨，*，/柜某，%嗽元，++，--

        比較運(yùn)算>,<喂击，==  結(jié)果返回boolean

        邏輯運(yùn)算&&剂癌，||，翰绊！
        && 兩邊都為true佩谷，結(jié)果為true
        || 只有一邊為true，結(jié)果為true
        监嗜！ 取反

        先將數(shù)據(jù)轉(zhuǎn)為number谐檀，再進(jìn)行比較
        */

       var a = 10;
       var b = 20;
       var c = 30;
       var d = 40;
       console.log(a*b);
       console.log(a/b);
       console.log(a%b);
       c++;
       console.log(c);
       d--;
       console.log(d);
       console.log(c%d);
       console.log(a<b && b<c);
       console.log(a<b || b>c);
        console.log(!(a>b));
    </script>

運(yùn)算.png

賦值，三目運(yùn)算

    <script>
        /*
        賦值運(yùn)算
        =裁奇，+=稚补，-=，*=框喳，/=课幕，%=
        三目運(yùn)算
        var f = (d<c)>
        */
       var a = 10;
       var b = 20;
       b +=a;
       // b=b+a;
       console.log(b); // 30
       b -=a;
       // b=b-a
       console.log(b); //20

       var c = 20;
       var d = 30;
       var f = (d>c)?"d大于c":"d小于c";
       console.log(f);
    </script>

賦值，三目運(yùn)算.png