JavaScript callback function

Question

please help I have a simple example here

<script type="text/javascript" language="javascript">
    function test(callback1) {
        callback1();
    }
    var f1 = function () {
        alert(1);
    }
</script>

Currently, parameter of the test function is a function, when abc button is clicked, test function will be called and then test will call f1. Everything okie with me.

However, I'd like a small change like this: parameter of the test function will be a string, I mean it should be a function name, test('f1') instead of test(f1). Is it possible?How can I implement this?

Thanks

possible duplicate of [JavaScript function name as a string...](http://stackoverflow.com/questions/359788/javascript-function-name-as-a-string) — epascarello, Dec 13 '10 at 15:13

score 2 · Answer 1 · answered Dec 13 '10 at 15:15

eval() is unneeded here. To pass a callback, just pass the function name. Functions are variables.

For example:

function test(a){
    alert(a);
}

function callback(b,a){
    b(a);
}

callback(test, 'dog'); //alerts 'dog'

So, in your code, test(f1) will work fine.

score 2 · Accepted Answer · answered Dec 13 '10 at 15:17

window[callback1]();

Depending on use I would prefer prepare separate functions map.

var funcMap = {
   f1: function() {...},
   ...
};
funcMap['f4'] = function() {...};
function test(callback1) {
    funcMap[callback1]();
}

It definitely doesn't bloat window namespace and is more secure (window has more methods provided by browser).

Don't use eval - it's evil!

score 0 · Answer 3 · answered Dec 13 '10 at 15:09

0

You can use eval() to execute the function which is passed as a string. But its deprecated to use eval.

Example:

function test(someFunctionName) {
        eval(someFunctionName);
    }

answered Dec 13 '10 at 15:09

Mahesh Velaga

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@epascarello: I haven't used it ever in production code, so I don't know how evil it can be. But, if many wise people tried it and say it is, then I go with them :) – Mahesh Velaga Dec 13 '10 at 15:17
if people say jump off a bridge because it is the quickest way down would you do it? :) Eval is slow, eval can lead to security issues, and there are better solutions. – epascarello Dec 13 '10 at 15:36
@epascarello: I won't. I certainly don't want to re-invent the wheel, I learn from other's experience as well, otherwise you will never move forward than where others have landed in the past. I take suggestions if they make sense to me :). Also I clearly stated in my answer that eval is deprecated. – Mahesh Velaga Dec 13 '10 at 22:23

score 0 · Answer 4 · answered Dec 13 '10 at 15:10

0

write something like

function test(callback1) {
    eval(callback1 + "()");
}

then callback1 should be a string

answered Dec 13 '10 at 15:10

Lukas Eder

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I know. But the pragmatic developer may always prefer evil to another 3hrs of searching :) – Lukas Eder Dec 13 '10 at 16:40
1

Pragmatic programmer should also educate followers by doing research, which isn't so hard here. Eval is like SQL parametrized by concatenated strings. I wouldn't call one a programmer when using them. – gertas Dec 13 '10 at 22:13

JavaScript callback function

4 Answers4