【代码笔记】Web-JavaScript-JavaScript 类型转换

来源：cnblogs　　作者：菜鸟and小白　　时间：2018/12/27 10:34:21　　对本文有异议

一，效果图。

二，代码。

<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
    <title>JavaScript 类型转换</title>
</head>
<body>
    <!--typeof操作符-->
    <p> typeof 操作符返回变量、对象、函数、表达式的类型。</p>
    <p id="demo"></p>
    <script>
    document.getElementById("demo").innerHTML =
        typeof "john" + "<br>" +
        typeof 3.14 + "<br>" +
        typeof NaN + "<br>" +
        typeof false + "<br>" +
        typeof [1, 2, 3, 4] + "<br>" +
        typeof {
            name: 'john',
            age: 34
        } + "<br>" +
        typeof new Date() + "<br>" +
        typeof
    function() {} + "<br>" +
    typeof myCar + "<br>" +
        typeof null;
    </script>
    <!--constructor 属性-->
    <p>constructor属性返回变量或对象的构造函数.</p>
    <p id="demo1"></p>
    <script>
    document.getElementById("demo1").innerHTML = "john".constructor + "<br>" + (3.14).constructor + "<br>" + false.constructor + "<br>" + [1, 2, 3, 4].constructor + "<br>" + {
        name: "john",
        age: 34
    }.constructor + "<br>" + new Date().constructor + "<br>" + function() {}.constructor;
    </script>
    <!--constructor 属性-->
    <p>判断是否为数组。</p>
    <p id="demo2"></p>
    <script>
    var fruits = ["Banana", "Orange", "Apple", "Mango"];
    document.getElementById("demo2").innerHTML = isArray(fruits);
    function isArray(myArray) {
        return myArray.constructor.toString().indexOf("Array") > -1;
    }
    </script>
    <p>判断是否为日期。</p>
    <p id="demo3"></p>
    <script>
    var myDate = new Date();
    document.getElementById("demo3").innerHTML = isDate(myDate);
    function isDate(myDate) {
        return myDate.constructor.toString().indexOf("Date") > -1;
    }
    </script>
    <p>String()方法可以将数字转换为字符串</p>
    <p id="demo4"></p>
    <script>
    var x = 123;
    document.getElementById("demo4").innerHTML = String(x) + "<br>" + String(123) + "<br>" + String(100 + 23);
    </script>
    <p>toString()方法将数字转为字符串</p>
    <p id="demo5"></p>
    <script>
    var x = 123;
    document.getElementById("demo5").innerHTML = x.toString() + "<br>" + (123).toString() + "<br>" + (100 + 23).toString();
    </script>
    <p> typeof 操作符返回变量或表达式的类型。</p>
    <button onclick="myFunction()">点我</button>
    <p id="demo6"></p>
    <script>
    function myFunction() {
        var y = "5";
        var x = +y;
        document.getElementById("demo6").innerHTML =
            typeof y + "<br>" + typeof x;
    }
    </script>
    <p>typeof操作符返回变量或表达式的类型</p>
    <button onclick="myFunction()">点我</button>
    <p id="demo7"></p>
    <script>
    function myFunction() {
        var y = "john";
        var x = +y;
        document.getElementById("demo7").innerHTML = typeof + "<br>" + x;
    }
    </script>
</body>
</html>