JavaScript - How do I call a function from a string name and pass an array object?

Question

I've got a user control which lets users provided their own script names that are called by the control on specific events.

I have the following code:

initialize : function()
{

    // Call the base initialize method
    Point74.WebAutoComplete.callBaseMethod(this, 'initialize');

    $(document).ready(
        Function.createDelegate(this, this._onDocumentReady)
    );

},

_onDocumentReady : function()
{
    var me = this;
    $("#" + me.get_id()).autocomplete(me.get_ashxAddress(), 
        { 
            formatItem: function(item)
            {
                return eval(me.get_formatFunction() + "(" + item + ");");
            }
        } 
    ).result(me.get_selectFunction());
}

me.get_formatFunction contains the name of a function, i.e. "FormatItem". This example is currently using eval, which I do not want to use... plus this example doesn't work anyway, but I thought I'd show what I'm trying to get at.

In the example above, I get a value undefined error as 'item' is a string array and eval tries to convert it into one long string.

How can I achieve this functionality any still pass through 'item' as a string array to the named function?

If passing named functions is a bad idea, are there any alternatives?

This is how my control is declared:

<p74:WebAutoComplete runat="server" ID="ato_Test" AshxAddress="WebServices/SearchService.ashx" 
     FormatFunction="formatItem" SelectFunction="searchSelectedMaster" />

How many times per week is this going to get asked? First dup: http://stackoverflow.com/questions/359788/javascript-function-name-as-a-string — Crescent Fresh, Oct 09 '09 at 17:17
Another dup: http://stackoverflow.com/questions/1144297/ways-to-call-a-javascript-function-using-the-value-of-a-string-variable/1144334#1144334 — Crescent Fresh, Oct 09 '09 at 17:18

score 3 · Accepted Answer · answered Oct 09 '09 at 16:28

3

me[me.get_formatFunction()](item);

answered Oct 09 '09 at 16:28

Mike Blandford

3,952
4
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THe only difference to this was that I had to use window[] instead of me[]. – djdd87 Oct 12 '09 at 08:24
Yeah, if you define it as a global function then you use window[]. If you define it on an object prototype referred to by me, then you use me[] – Mike Blandford Oct 12 '09 at 14:56

score 1 · Answer 2 · edited Jan 05 '14 at 15:35

1

I'm not sure what your overall plan is, but you can pass functions around themselves instead of their names:

function Foo(x, y) {
  // do something
}

function Bar(f, a, b) {
  // call Foo(a,b)
  f(a,b);
}

Bar(Foo, 1, 2);

edited Jan 05 '14 at 15:35

BenMorel

34,448
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answered Oct 09 '09 at 16:25

x0n

51,312
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score 1 · Answer 3 · answered Oct 09 '09 at 16:39

If your intent is to pass all arguments to the user-specified function that are passed to formatItem(), then instead of using:

formatItem: function(item)
{
 return eval(me.get_formatFunction() + "(" + item + ");");
}

Use:

formatItem: function()
{
 return me.get_formatFunction().apply(me, arguments));
}

The apply() method can be called on a function object, in order to invoke that function using the specified "this" and argument array. See: http://odetocode.com/blogs/scott/archive/2007/07/04/function-apply-and-function-call-in-javascript.aspx for an explanation of the call() and apply() functions in javascript.

Then you will want get_formatFunction() to return a function object, rather than just the name of the function; or you can try:

me[me.get_formatFunction()]

...to get a function which is defined on 'me' by its name. (Note that if get_formatFunction() returns the string 'myFunc', then this is equivalent to me.myFunc)

[Edit: changed references to 'this' to use 'me' instead]

window[get_formatFunction()] will work if the function is defined in global scope. It might have been defined as an object prototype. — Mike Blandford, Oct 09 '09 at 16:43

JavaScript - How do I call a function from a string name and pass an array object?

3 Answers3