Question

我想动态创建一个闭包。请参阅以下代码以获取解释。

function myFunction(){
    parentScopedVar(); //Would like to be able to call without using 'this'.
}


function myDynamicFunc(dynamicClosure){

    //What do I need to do here to dynamically create 
    //a var called 'parentScopedVar' that can be referenced from myFunction?

    myFunction.call(self);
}


myDynamicFunc(
         {
             parentScopedVar : function() { alert('Hello World'); }
         });

Answer 1

Javascript使用lexical scope（基于声明代码的位置），而不是动态范围。

如果您决定尝试做一些语言并不真正鼓励的事情，您可以使用eval(string of code here)强制在当前执行上下文中评估一串代码。事实上，你可以使用eval()做各种奇怪的事情，但我更倾向于以一种利用Javascript优势的方式编写代码，而不是使用违背主要设计主题的编码风格。语言（我的意见）。

我并不完全清楚你要解决的问题是什么，但你可以将函数作为参数传递，然后通过被调用函数中的参数调用它。

// declare your function that takes a function reference an argument
function myFunction(callback) {
    // call the function that was passed
    callback();
}

function myDynamicFunc(){

    // declare a local function
    function myAlert() {
        alert('Hello World');
    }

    // call your other function and pass it any function reference
    myFunction(myAlert);
}

这不会传递整个执行上下文。为此，您必须在对象中打包上下文并传递对象的引用，然后从对象中取消引用属性。这通常是您在JS中传递环境的方式。

您可以使用本地声明的函数来提供对回调（同样是词法范围）的父作用域的访问：

// declare your function that takes a function reference an argument
function doSomething(callback) {
    // call the function that was passed
    callback();
}

function myFunc() {
    var myLocal1 = "Hello";
    var myLocal2 = "World";

    function callback() {
        // when this is called, it has access to the variables of the parent scope
        alert(myLocal1 + " " + myLocal2);
    }

    doSomething(myFunc);
}

您甚至可以将其用作持久封闭：

// declare your function that takes a function reference an argument
function doSomething(callback) {
    // call the function that was passed
    callback();
}

function myFunc() {
    var myLocal1 = "Hello";
    var myLocal2 = "World";

    function callback() {
        // when this is called, it has access to the variables of the parent scope
        // which are still alive in this closure even though myFunc has finished
        // executing 10 minutes ago
        alert(myLocal1 + " " + myLocal2);
    }

    // call the callback function 10 minutes from now, 
    // long after myFunc has finished executing
    setTimeout(callback, 10 * 60 * 1000);
}

以下是Javascript中词汇和动态范围的一些参考文章：

Is it possible to achieve dynamic scoping in JavaScript without resorting to eval?

Are variables statically or dynamically "scoped" in javascript?

What is lexical scope?

Javascript调用动态关闭

1 个答案: