Avoid using eval() on Javascript

Javascript’s eval() function is evil. Its performance is bad, and it’s very difficult to debug. If you ever use it the goto raptor will come for you…

OK, now I know why not to use eval() but… How could I avoid that evil function in my code?

The 3 main uses I’ve found for eval() are:

Assign a property to an object when you have its name calculated in a variable
Call a function when you’ve it’s name calculated in a variable
Create an object from a class when you’ve it’s name calculated in a variable

To sum up, do any access of any kind to any object’s property when you’ve this property name in a variable. This kind of access can be accomplished using this notation.

var property = "property_name"; var object = new Object() alert(object[property]) //will alert object.property_name alert(object["property_name"]); //will alert object.property_name alert(window["object"]["property_name"]) //will alert object.property_name

If you don’t believe it, just copy&paste the previous code on Firebug and see how it works.

So, let’s now see an example on the previous cases

//assign a property to an object when //you have its name calculated in a variable var property_name = "a_great_property" var object = new Object(); object[property_name] = "Hello world!"; alert(object.property_name); //will alert Hello world! //call a function when you’ve it’s name //calculated in a variable var function_name = "whatever_function"; var object = { whatever_function: function(){ alert("Hello world!"); } } object[function_name_](); // will alert Hello world! //create an object from a class when //you've it's name calculated in a variable var klass_name = "Object"; var object = new window[klass_name];

Those were just a couple of basic examples that I could remember, but I’m quite sure that there are much more other evil uses of eval() out there that you can destroy :D