ES02 变量数组对象方法

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1 变量

  1.1 变量的声明

    利用var关键字来声明变量,例如:

    var a = 100;
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1">
<title>javascriptTest</title>
<meta name="description" content="">
<meta name="keywords" content="">
<link href="" rel="stylesheet">

<!-- <script src="/js/jquery.js"></script> -->
<script src="http://cdn.static.runoob.com/libs/jquery/2.0.0/jquery.min.js"></script>
<script>
    var a = 100;
    function test01() {
        alert("变量a的值为:" + a);
    }
</script>
    
</head>
<body>
    <p id="testP">Hello Boy</p>
    
    <button id="test" onClick="test01()">测试按钮</button><br />

    <script>
    
    </script>

    
</body>
</html>
View Code

  1.2 变量的作用域

    1.2.1 局部作用域

      在函数中声明的作用域叫做局部作用域

    1.2.2 全局作用域

      在函数之外声明的作用与叫做全局作用域

    1.2.3 区别

      局部作用域中可以获取全局变量,但是局部变量只能在局部作用域中使用,即:局部变量只能在声明它的方法中使用

      

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1">
<title>JavaScriptTest</title>
<meta name="description" content="">
<meta name="keywords" content="">
<link href="" rel="stylesheet">

<!-- <script src="/js/jquery.js"></script> -->
<script src="http://cdn.static.runoob.com/libs/jquery/2.0.0/jquery.min.js"></script>
<script>
    var a = "全局变量a";
    function test01() {
        var b = "局部变量b";
        alert("test01方法 -> " + a);
        alert("test01方法 -> " + b);
    }
    function test02() {
        alert("test02方法 -> " + a);
        alert("test02方法 -> " + b);
    }
</script>
    
</head>
<body>
    <p id="testP">Hello Boy</p>
    
    <button id="test01" onClick="test01()">测试按钮01</button><br />
    <button id="test02" onClick="test02()">测试按钮02</button>

    <script>
    
    </script>

    
</body>
</html>
View Code

      坑01:在局部作用域中如果使用的变量未i进行声明操作就会到全局中去寻找对应的全局变量,如果没找到就会创建一个全局变量

      

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1">
<title>JavaScriptTest</title>
<meta name="description" content="">
<meta name="keywords" content="">
<link href="" rel="stylesheet">

<!-- <script src="/js/jquery.js"></script> -->
<script src="http://cdn.static.runoob.com/libs/jquery/2.0.0/jquery.min.js"></script>
<script>
    var a = "全局变量a";
    function test01() {
        b = "Hello Boy"
        alert("test01方法 -> " + a);
        alert("test01方法 -> " + b);
    }
    function test02() {
        alert("test02方法 -> " + a);
        alert("test02方法 -> " + b);
    }
</script>
    
</head>
<body>
    <p id="testP">Hello Boy</p>
    
    <button id="test01" onClick="test01()">测试按钮01</button><br />
    <button id="test02" onClick="test02()">测试按钮02</button>

    <script>
    
    </script>

    
</body>
</html>
View Code

 

2 数组

  2.1 数组的声明

    2.1.1 利用 Array 对象进行声明

var list01 = new Array();

    2.1.2 利用 [ ] 进行声明

var list01 = [];

  2.2 数组的赋值

    数组名[数组元素索引]

list01[0] = "warrior";
list01[4] = "fury";

    坑01:中间为进行初始化的数组元素自动赋值为 undefined

  2.3 数组的声明和赋值

    2.3.1 利用 Array 对象实现

var list01 = new Array("warrior", "fury", "重庆火锅");

    2.3.2 利用 [ ] 实现

var list01 = ["warrior", "fury", "重庆火锅", "小面"];
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1">
<title>JavaScriptTest</title>
<meta name="description" content="">
<meta name="keywords" content="">
<link href="" rel="stylesheet">

<!-- <script src="/js/jquery.js"></script> -->
<script src="http://cdn.static.runoob.com/libs/jquery/2.0.0/jquery.min.js"></script>
<script>
    var list01 = ["warrior", "fury", "重庆火锅", "小面"];
    function test01() {
        for (var i = list01.length - 1; i >= 0; i--) {
            console.log(list01[i]);
        }
    }
    function test02() {
        
    }
</script>
    
</head>
<body>
    <p id="testP">Hello Boy</p>
    
    <button id="test01" onClick="test01()">测试按钮01</button><br />
    <button id="test02" onClick="test02()">测试按钮02</button>

    <script>
    
    </script>

    
</body>
</html>
View Code

 

3 对象

  3.1 对象的声明

    3.1.1 利用 Object 

var obj = new Object()

    3.1.2 利用 { } 

var obj = {};

  3.2 对象的赋值

    obj.name = "warrior";
    obj.address = "重庆市";

  3.3 对象的声明和赋值

    3.3.1 利用Object

    var obj = new Object({
        name: "warrior",
        address: "重庆",
        age: 123
    });

    3.3.2 利用 { } 

    var obj = {
        name: "warrior",
        address: "重庆"
    };

 

4 方法

    function onCompute() {
        alert("hello boy");
        var a = document.getElementById("a");
        var b = document.getElementById("b");
        document.getElementById("result").value = Number(a.value) + Number(b.value);
    }
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1">
<title>JavaScriptTest</title>
<meta name="description" content="">
<meta name="keywords" content="">
<link href="" rel="stylesheet">

<!-- <script src="/js/jquery.js"></script> -->
<script src="http://cdn.static.runoob.com/libs/jquery/2.0.0/jquery.min.js"></script>
<script>
    
    function onCompute() {
        alert("hello boy");
        var a = document.getElementById("a");
        var b = document.getElementById("b");
        document.getElementById("result").value = Number(a.value) + Number(b.value);
    }


    function test01() {
    }
    function test02() {
        
    }
</script>
    
</head>
<body>
    <input type="number" id="a" placeholder="加数01" />
    &nbsp;
    <span> + </span>
    &nbsp;
    <input type="number" id="b" placeholder="加数02" />
    &nbsp;
    <span> = </span>
    &nbsp;
    <input type="number" id="result" placeholder="结果" />
    &nbsp;
    <button id="compute" onclick="onCompute()">计算</button>
    <hr />
    
    <button id="test01" onClick="test01()">测试按钮01</button><br />
    <button id="test02" onClick="test02()">测试按钮02</button>

    <script>
    
    </script>

    
</body>
</html>
View Code

  4.1 有参方法

    坑01:由于JavaScript是动态类型语言,所以在定义方法时的形参不用指定类型,用合法的变量名指明就行啦

    function test01(a, b) {
        alert(a);
        alert(b);
    }

  4.2 带返回值的方法

    function test02(a, b) {
        alert(test03(a, b));
    }
    function test03(a, b) {
        return a + b;
    }
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1">
<title>JavaScriptTest</title>
<meta name="description" content="">
<meta name="keywords" content="">
<link href="" rel="stylesheet">

<!-- <script src="/js/jquery.js"></script> -->
<script src="http://cdn.static.runoob.com/libs/jquery/2.0.0/jquery.min.js"></script>
<script>
    
    function onCompute() {
        alert("hello boy");
        var a = document.getElementById("a");
        var b = document.getElementById("b");
        document.getElementById("result").value = Number(a.value) + Number(b.value);
    }


    function test01(a, b) {
        alert(a);
        alert(b);
    }
    function test02(a, b) {
        alert(test03(a, b));
    }
    function test03(a, b) {
        return a + b;
    }
</script>
    
</head>
<body>
    <input type="number" id="a" placeholder="加数01" />
    &nbsp;
    <spanES6解构赋值

ES6解构

ES5数组对象常用方法总结

260 ES6解构赋值

再不学ES6你就out啦

ES6(变量的解构赋值)