为什么我可以在 javascript 中定义相同的函数两次？

Question

I have a javascript file in which I write a bunch of jquery functions. I have a function to return the angular scope. I found out that if I were to write the same function twice, the code still executes.

function getngScope()
{
    alert(2);
    return angular.element($('#data-area')).scope();
}

function getngScope()
{
    alert(1);
    return angular.element($('#data-area')).scope();
}

When I call getngScope() I get "1" alerted and the scope returned. Why does it have this behavior?

Answer 1

The second definition of an Object overwrites the first one. In general the last definition of an object overwrites all previous definitions.

Functions in JavaScript are Objects:

(function () {}) instanceof Object === true

When you create a new global function f it's equivalent to creating a property in the window object and assigning the function definition to that variable, if you create a function:

function myFun() { console.log('my function') };

and then check the value of window.myFun you'll notice it is the same function as myFun :

window.myFun === myFun // true

You'll also notice that modifying window.myFun changes/overwrites myFun .

Eg

 function myFun() { console.log('myFun') }; myFun(); // Prints: 'myFun' // Overwrite myFun window.myFun = function () { console.log('NoFun') }; myFun(); // Prints: 'NoFun'

The second definition of the function takes precedence.

I recommend you read the chapter on Functions from JavaScript: the good parts by Crockford.

Answer 2

函数是内存堆栈中的数据，因此当您定义另一个同名函数时，它会覆盖前一个函数。

Answer 3

Well obviously you're not meant to define the same function twice. However, when you do, the latter definition is the only 1 that applies. Try not to do that. Find another way other than giving two functions the same name.

Answer 4

第二个函数取代了第一个函数，您可以随时通过修改函数名称来更改它，如果不是，您可以添加多个参数..如果需要的话...以及对这种行为的解释，与其他编程语言不同javascript 在执行时不会返回任何错误..所以你可以假设它只是在执行过程中通过覆盖函数来纠正自己。