handwriting-algorithm/07apply.html at master · ustcfury/handwriting-algorithm · GitHub

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<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <script>
        // apply 函数实现
        Function.prototype.myApply = function (context) {
            // 判断调用对象是否为函数
            if (typeof this !== "function") {
                throw new TypeError("Error");
            }
            let result = null;
            // 判断 context 是否存在，如果未传入则为 window
            context = context || window;
            // 将函数设为对象的方法
            context.fn = this;
            // 调用方法
            if (arguments[1]) {
                result = context.fn(...arguments[1]);
            } else {
                result = context.fn();
            }
            // 将属性删除
            delete context.fn;
            return result;
        };
    </script>
</body>

</html>