Dynamically Setting a JavaScript Object's Method's Source

Question

I've recently been working on a nice little JavaScript game engine that works a lot like Game Maker, but lets people create basic JavaScript games within a browser. Every instance of every object will have it's own preset methods, which the runner will iterate through and execute. I'm trying to find a way to let the user / creator dynamically edit any of the methods source code. When I say 'preset methods', I mean blank methods stored under specific preset names within the objects / object instances. Here's a basic example:

var newObject = object_add("object_name"); // Adds a new object 'blueprint' and returns the reference.

The function object_add(); creates a JavaScript object, and adds a number of preset methods to it, such as:

create
destroy
step
draw

.. and many more

Each of these methods will have no code in them to start with. I need to let the creator dynamically change any of the methods source code. I could simply overwrite the variable that points towards the method, with a new method, but how can you set method's source code using a string?

I know that something like:

newObject.create = function(){textbox.innerHTML};

definitely wouldn't work. Any ideas?

Many thanks,

Dan.

I've been looking at closures, but don't really understand how they work. If i did something like: function changeSource(object,method,newcode){ object[method]=function(){newcode}; } would newcode become the actual source within that function, or not? — Daniel Price
– Daniel Price, Commented Apr 17, 2014 at 10:49
possible duplicate of Creating functions dynamically in JS (Found by simply googling for dynamically create javascript function from code ...) — C3roe
– C3roe, Commented Apr 17, 2014 at 10:50

S1cK94 · Accepted Answer · 2014-04-17 10:35:48Z

1

Looks like you want to use eval function, but it's generally a bad idea.

answered Apr 17, 2014 at 10:35

S1cK94

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4 Comments

Daniel Price Over a year ago

I'm trying to refrain from using eval, thank you for the suggestion though.

jfriend00 Over a year ago

@DanielPrice - don't know how you dynamically set the source of a method from a user generated string without using eval() or manually creating a script tag with the source in it (which is not really any different than using eval()).

C3roe Over a year ago

You want to dynamically create function objects from code in string form, so whether or not you are using eval or any other method does not really make a difference.

Daniel Price Over a year ago

I'm sure eval would be a lot slower to run than actual functions, as javascript has to evaluate the code before executing it.

Community · Accepted Answer · 2017-05-23 11:49:55Z

0

The answer was found at: Creating functions dynamically in JS

Here's the answer (copied from the other page).

Well, you could use Function, like in this example:

var f = new Function('name', 'return alert("hello, " + name + "!");');
f('erick');
//This way you're defining a new function with arguments and body and assigning it to a variable f. You could use a hashset and store many functions:

var fs = [];
var fs['f1'] = new Function('name', 'return alert("hello, " + name + "!");');
fs['f1']('erick');
//Loading xml depends if it is running on browser or server.

Thanks, @CBroe https://stackoverflow.com/users/1427878/cbroe

edited May 23, 2017 at 11:49

CommunityBot

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answered Apr 17, 2014 at 10:55

Daniel Price

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