Javascript code as a variable

Question

Ok, this may sound a bit crazy but hear me out :)

I would like to do the following in javascript:

define START_OF_EVERY_FUNCTION = "try {"
define END_OF_EVERY_FUNCTION   = "} catch () {}"

function TEST () {
    START_OF_EVERY_FUNCTION
    // rest of function
    END_OF_EVERY_FUNCTION
}

Basically, can I define a list of javascript lines (code) and include them as above? I'm looking for a technique versus comments about whether this is a good idea or not or debate over wrapping all functions in a try/catch block.

I know about eval(), but I dont think you can eval statements like the above.

I think I get what you are trying to do, which is to use pre-written snippets to build new functions, while I'm not sure this is a great approach, I think the best way to accomplish this is to use a server-side language as a sort of "compiler", where you have a small templating language that you use in javascript, just something like {{snippet1}} and then use a server-side language that will go through and replace every instance of {{snippet1}}, for example, with the corresponding code snippet, then you can re-run it anytime anything changes and you have your jscript files updated — Rick
– Rick, Commented Sep 7, 2010 at 9:00

Jage · Accepted Answer · 2010-03-05 06:29:10Z

4

This might be goofy but you could define a master function and run other functions through it by passing them in.

var execute = function(func){
    alert('before');
    func();
    alert('after');
};

function sayHi(){
    alert('hi there');
}

execute(sayHi);

As requested, an example with passing arguments.

var execute = function(func){
    alert('before');
    var ret = func.apply(null, Array.prototype.slice.call(arguments, 1));
    alert('after');
};

function saySomething(sayWhat){
    alert(sayWhat);
}

execute(saySomething,'hey there');

edited Mar 5, 2010 at 6:29

answered Mar 5, 2010 at 4:17

Jage

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3 Comments

John K Over a year ago

This might be more like the "Javascript way".

Asaph Over a year ago

Can you provide an example that passes arguments to the function?

John K Over a year ago

@Asaph: Consider the arguments array that is part of a called function developer.mozilla.org/En/Core_JavaScript_1.5_Reference/…

Anthony Forloney · Accepted Answer · 2010-03-05 04:13:50Z

1

That is not allowed in JavaScript.

answered Mar 5, 2010 at 4:13

Anthony Forloney

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2 Comments

Jack Over a year ago

Yes, clearly - but is there a technique that can achieve that goal?

Anthony Forloney Over a year ago

As far as I know, no. It looks like you are trying to simulate a macro, and I believe macros are used with complier languages, not interpreted.

Jonathan · Accepted Answer · 2010-03-05 04:40:40Z

1

You could extend the Function prototype:

Function.prototype.tryThis = function() {
    try {
        this();
    }catch(ex){
        alert('Caught '+ex);
    };
};

function tryIt() {
    alert('Inside tryIt');throw "My Error from tryIt";
}

tryIt.tryThis();

answered Mar 5, 2010 at 4:40

Jonathan

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Comments

nickytonline · Accepted Answer · 2010-03-05 04:14:45Z

0

You need to look into aspect oriented programming for JavaScript. You can create hooks for function entry and exit. Tools like JSUnit do this for example.

answered Mar 5, 2010 at 4:14

nickytonline

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Comments

nickf · Accepted Answer · 2010-03-05 04:18:47Z

I think you can do this with the "new Function" operator. I've never used it myself, since I'm not clinically insane, but I believe you can pass it a string which it will evaluate and use as the function body. You can also get the code for each function by calling myFunction.toString(). So put together, it'd be something like this:

var functionsToMessUp = ['myFunc1', 'myFunc2'];

for (var i = 0; i < functionsToMessUp.length; ++i) {
    var theFunc = window[functionsToMessUp[i]]; // assuming they're in global scope
    window[functionsToMessUp[i]] = new Function(
        START_OF_EVERY_FUNCTION
        + theFunc.toString()
        + END_OF_EVERY_FUNCTION
    );
}

Now, the above almost certainly won't work - there's parameters and other things to take into consideration, and I don't even think that's how the new Function constructor works, but if you really want to go down this path (which I really don't recommend), then this might be a good starting point for you.

Jimmy · Accepted Answer · 2010-03-05 04:22:12Z

0

Maybe something like this?

function tryCatch(callback) {
  try {
    callback();
  } catch() {}
}

var myFunction = function() {
  // do some stuff
};

tryCatch(myFunction);

answered Mar 5, 2010 at 4:22

Jimmy

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