How to implement refinement in JavaScript_问答_开发者

How to implement refinement in JavaScript

开发者 https://www.devze.com 2023-03-15 19:24 出处：网络

I am trying to implement (so-to-say) a refinement in JavaScript. Kindly look at the following example:

相关专题：javascript

I am trying to implement (so-to-say) a refinement in JavaScript. Kindly look at the following example:

<html>
<head>
<title>Function Override (Refinement) example</title>
<script type="text/javascript">

// original function
function oneFunc() {
    document.writeln("<p> In original oneFunc() </p>");
}

var prevOneFunc = null;
if (oneFunc) {
    prevOneFunc = oneFunc;
}

// redeclared function (should refine/complement the original one)
function oneFunc() { 
    if (prevOneFunc) {
        prevOneFunc(); // should call original oneFunc(), BUT IT ISN'T
    }
    document.writeln("<p> In refined oneFunc() </p>");
}

oneFunc();

</script>
</head>
<body>
</body>
</html>

My intention was to have two printouts:

In origina开发者_如何转开发l oneFunc()
In refined oneFunc()

However, it seems that since at the moment of execution oneFunc refers to the new/refined function, hence the output is different than expected. In the debugger checked that I am entering into the infinite recursion :) (yes, understood why exactly).

Please explain which information I am missing to implement it properly.

Update: A few limitations: I think (not sure) that I can't modify the original oneFunc declaration and it is declared just like described above. I shouldn't modify the declaration of the refined oneFunc either.

This works: http://jsfiddle.net/maniator/gxpK8/

When you do it your way you are defining:

prevOneFunc = function oneFunc(){...}

So you are not assigning a anonymous function, therefore to do what you want to do you have to declare oneFunc like so:

oneFunc = function() {
    document.writeln("<p> In original oneFunc() </p>");
}

Then later on it is correct:

prevOneFunc = function(){...}

I would use a closure. It avoids (another) global property and shows intent better, at least to me.

// original function
function oneFunc() {
   return "world"
}

alert(oneFunc)

oneFunc = (function (original) {
   // a closure will prevent the original function -- which is an object
   // from ever being lost
   return function () { 
      alert("before");
      var ret = original()
      alert("after")
      return "hello " + ret
   }
})(oneFunc)

alert(oneFunc)

Happy coding

For comment:

The exact same applies. Functions are just objects. The only "trick" is making sure someone else calls your object. If the function is a property (as in the code shown) then it's easy:

window.somefunc = myfunc

someobj.somefunc = myfunc

The only case when it's not easy (really possible) is when the function has been bound in some for of closure or otherwise accessed via a different mechanism.

http://jsfiddle.net/tylermwashburn/6Fu8Q/

That should do what you want. :)

That is because of JavaScript hoisting. http://www.adequatelygood.com/2010/2/JavaScript-Scoping-and-Hoisting

Try this:


var oneFunc = function(){ 
//In original oneFunc 
};

var prevOneFunc = null;
if (oneFunc) {
    prevOneFunc = oneFunc;
}

oneFunc = function(){
//In refined oneFunc 
};

oneFunc();