javascript - 传递一种方法供以后评估

Question

如果我将一个函数作为参数传递，并且该函数是一个 jQuery 方法，稍后调用传递的函数是否仍会正确设置 this？我以为会，但稍后调用该函数有 this = Window。

示例代码:

var $input = $('input').first();

var evaluators = [];

evaluators.push($input.val);

_.forEach(evaluators, function(valueMethod) {
    return valueMethod() //returns undefined always since this = window
}).

Answer 1

尝试使用 bind :

The bind() method creates a new function that, when called, has its this keyword set to the provided value, with a given sequence of arguments preceding any provided when the new function is called.

evaluators.push($input.val.bind($input)); 

值得注意的是bind是not supported on older browsers (例如 IE8 和 FF3(或更早版本))。