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  • parseInt/类型转换/字符串

    1.pa'rseInt整型

    1.1parseInt必须以数字开头的

    var topVal = parseInt("28px");
            console.log(topVal);
            //28

    1.2非数字开头时,控制器打印出来是NaN

    var z = parseInt("abc52");
            console.log(z);
            //NaN

    1.3两个参数情况下,16进制

    console.log(parseInt("0xf", 16))
            //15

    2.parseFloat浮点数

    var e = parseInt("12.34.26");
            console.log(e)
            //12
            var d = parseFloat("12.34.26");
            console.log(d);
            //12.34
    var b = parseInt("0123abc");
            console.log(b);
            //123
            var dd = parseFloat("0123abc");
            console.log(dd);
            //123
            var ee = Number("0123abc");
            console.log(ee);
            //NaN
            var cc = Number("18");
            console.log(cc);
            //18

    注意:当把一个字符串中数字提取出来,最好用parseInt或者parseFloat,前提条件必须是数字开头(125abc),而不是其他开头(abc123);不太推荐Number强制转换

    2.转换为字符串  string与toString

    <h2>转换为字符串类型</h2>
        <script>
            var ids = 65352;
            var idstr = ids.toString();
            console.log(idstr);//65352
            console.log(typeof idstr)//string
            console.log(String(ids))//65352
        </script>

    3.转为布尔Boolean

    <h2>转换为布尔类型</h2>
        <script>
            var ids = true;
            var idstr = false;
            console.log(typeof ids);//boolean
            console.log(typeof idstr)//boolean
        </script>

    3.1类型转换 

    (1)除0之外的所有数字,转换为布尔型都为true

    (2)除""之外的所有字符,都转为布尔型都为true

    (3)null和undefined转换为布尔型为false

    <h2>除0之外的所有数字,转换为布尔型都为true</h2>
        <script>
            var x = 0;
            var y = 1;
            console.log(Boolean(x));//false
            console.log(Boolean(y))//true
        </script>
    <h2>除""之外的所有字符,都转为布尔型都为true</h2>
        <script>
            var stringWords = "welcome";
            var stringKong = "";//空的
            var kongge = " ";
            console.log(Boolean(stringKong));//false
            console.log(Boolean(stringWords))//true
            console.log(Boolean(kongge))//true  空格布尔型也是true
        </script>
    <h2>null和undefined转换为布尔型为false</h2>
        <script>
            var y;
            var x = null;
            console.log(Boolean(y))//false
            console.log(Boolean(x))//false
        </script>
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  • 原文地址:https://www.cnblogs.com/huanghuali/p/9609232.html
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