处理集合_映射数组_5

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>提取weapon数组的粗略方法</title>
    <script src="../unitl/test.js"></script>
    <style>
        #results li.pass {color:green;}
        #results li.fail {color:red;}
    </style>


</head>

<body>
    <ul id="results"></ul>

</body>

<script>

    const ninjas = [

        {name:"Yagyu",weapon:"shuriken"},
        {name:"Yoshi",weapon:"katana"},
        {name:"Kuma",weapon:"wakizashi"}

    ];

    const weapons = [];
    ninjas.forEach(ninja =>{
        weapons.push(ninja.weapon);
    });


    assert(weapons[0] === "shuriken" 
        && weapons[1] === "katana"
        && weapons[2] === "wakizashi"
        && weapons.length === 3,"The new Array contains all weapons"
        );

</script>
</html>

首先创建一个空数组,使用forEach方法遍历ninjas数组。然后,将每个ninja对象的weapon属性添加到weapons数组中。可以想象,基于已有数组的元素创建数组是非常常见的,
因此它具有一个特殊的名称:映射数组。主要思想是将数组中的每个元素属性映射到新数组的元素上。javascript的map函数可以实现便捷操作。

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>映射数组</title>
    <script src="../unitl/test.js"></script>
    <style>
        #results li.pass {color:green;}
        #results li.fail {color:red;}
    </style>


</head>

<body>
    <ul id="results"></ul>

</body>

<script>


    const ninjas = [
        {name:"Yagyu",weapon:"shuriken"},
        {name:"Yoshi",weapon:"katana"},
        {name:"Kuma",weapon:"wakizashi"}
    ];

    const weapons = ninjas.map(ninja=>ninja.weapon);
    assert(weapons[0] === "shuriken"
           && weapons[1] === "katana"
           && weapons[2] === "wakizashi"
           && weapons.length ===3, "The new Array contains all weapons!"
    );


</script>
</html>

本例子中引入的js: test.js

内置的map方法创建了一个全新的数组,然后遍历输入的数组。对输入数组的每个元素,在新建的数组上,都会基于回掉函数的执行结果创建一个对应的元素。

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