Question

从link开始，有一段代码：

Function.prototype.bind = function(oThis) {
    if (typeof this !== "function") {
        // closest thing possible to the ECMAScript 5
        // internal IsCallable function
        throw new TypeError( "Function.prototype.bind - what " +
            "is trying to be bound is not callable"
        );
    }

    var aArgs = Array.prototype.slice.call( arguments, 1 ),
        fToBind = this,
        fNOP = function(){},
        fBound = function(){
            return fToBind.apply(
                (
                    this instanceof fNOP &&
                    oThis ? this : oThis
                ),
                aArgs.concat( Array.prototype.slice.call( arguments ) )
            );
        }
        ;

    fNOP.prototype = this.prototype;
    fBound.prototype = new fNOP();

    return fBound;
};


function foo(p1,p2) {
    this.val = p1 + p2;
}

// using `null` here because we don't care about
// the `this` hard-binding in this scenario, and
// it will be overridden by the `new` call anyway!
var bar = foo.bind( null, "p1" );

var baz = new bar( "p2" );

console.log(baz.val); // p1p2

我在Chrome中运行这段代码。我得到了＆＃39; undenfined＆＃39;的输出，而不是＆＃39; p1p2＆＃39;的答案。列在书中

我发现，将 null 传递给bind函数是不正确的。传入 null 时，此位于代码行＆＃39; this.val = p1 + p2;＆＃39;等于＆＃39; 窗口＆＃39;而不是baz对象。

但是，如果我使用bind的内置函数，输出是正确的。我认为这段代码会产生巨大的误解。

有人可以给我更多澄清吗？

绑定函数示例在You-Dont-Know-JS的书中有错误

0 个答案: