ES6箭頭函數this指向和arguments知識

時間 2021-08-14

標籤 css html jquery chrome app ide 函數 this scala 欄目 JavaScript 简体版

原文原文鏈接

<!DOCTYPE html>
<html >
<head>
<meta charset="UTF-8">   
<meta http-equiv="X-UA-Compatible" content="IE=Edge,chrome=1"/>  
<meta name="viewport" content="width=device-width, initial-scale=1.0, minimum-scale=1.0, maximum-scale=1.0, user-scalable=no" />       
<title>箭頭函數</title>
<style type="text/css">
html {height: 100%;}
body {width: 200px;height: 100%;position: relative;padding: 0;margin: 0;}
</style>
</head>
<body>
<script src="https://cdn.bootcss.com/jquery/1.9.0/jquery.js"></script>
<script>
var obj = {
    data: ['beijing', 'shanghai'],
    init: function () {
        console.log(arguments[0].name);//xutongbao
        var test = () => {
            console.log(this.data);//["beijing", "shanghai"]
            console.log(arguments[0].name);  //xutongbao
        }
        test();        
    }
}
obj.init({name: 'xutongbao'});
var test = () => {
    console.log(arguments);  //未定義 ReferenceError: arguments is not defined
}
test({name: 'xutongbao'}); 
</script>
</body>
</html>

因爲this在箭頭函數中已經按照詞法做用域綁定了，因此，用call()或者apply()調用箭頭函數時，沒法對this進行綁定，即傳入的第一個參數被忽略：css

<!DOCTYPE html>
<html >
<head>
<meta charset="UTF-8">   
<meta http-equiv="X-UA-Compatible" content="IE=Edge,chrome=1"/>  
<meta name="viewport" content="width=device-width, initial-scale=1.0, minimum-scale=1.0, maximum-scale=1.0, user-scalable=no" />       
<title>箭頭函數</title>
<style type="text/css">
</style>
</head>
<body>
<script src="https://cdn.bootcss.com/jquery/1.9.0/jquery.js"></script>
<script>
var obj = {
    birth: 1990,
    getAge: function (year) {
        var b = this.birth; // 1990
        var fn = (y) => y - this.birth; // this.birth還是1990
        return fn.call({birth:2000}, year);
    }
};
var age = obj.getAge(2018); // 28
console.log(28)

</script>
</body>
</html>