How to pass variable to a callback function

Question

function firstCallme(iWantToBePassed) {

   post(callbackFun);
}

// This function shouldn't be anonymous.
function callbackFun(dataFromPostFun) {

 alert(iWantToBePassed);
}

How to pass the variable iWantToBePassed from firstCallme() to callbackFun()? There are several similiar question in SO. But I couldn't identify the solution from it.

I know only one solution as given below:

function firstCallme(iWantToBePassed) {

   post(function(data){callbackFun(data,iWantToBePassed) });
}

// This function shouldn't be anonymous.
function callbackFun(dataFromPostFun, iWantToBePassed) {

 alert(iWantToBePassed);
}

Is there any better solution?

UPDATE:

here:

function post(callbackFun) {
  jQuery.post('url', 'data', callbackFun, 'json');    
}

Can you explain what the post function is doing? Is that a server call and your callback is only meant to be invoked after the post is finished. — orandov, Dec 27 '12 at 12:15
The code you've given should work just fine, have you tried it? why can't callbackFun() be anonymous? — Ja͢ck, Dec 27 '12 at 12:23
@Jack I am calling the "callbackFun()" in one more function. If I make it anonymous i have to put the same code twice. — Mohammed H, Dec 27 '12 at 12:26
You could pass `callbackFun.bind(iWantToBePassed)` to the `post()` function; it will then be available as `this` inside. — Ja͢ck, Dec 27 '12 at 13:17

score 2 · Accepted Answer · edited May 23 '17 at 12:18

Since your callback function is invoked after a post then the only way to pass parameters to the callback function is to use some form of Closure like you showed in the solution you mentioned in your question.

You can also post your parameter iWantToBePassed and retrieve it from the data in the post in your callback function. But I wouldn't recommend this route unless you need that parameter on the server.

score 1 · Answer 2 · edited Dec 14 '13 at 18:46

Just call the callbackFun function with the parameter to should be passed.

The parameter after the function is what is posted, you don't have to tell the JavaScript browser to post something, it already knows it has to post (pass) a variable to a function when it is declared between the parentheses.

function firstCallme(iWantToBePassed) {
    callbackFun(iWantToBePassed);
}

function callbackFun(dataFromPostFun) {
   alert(dataFromPostFun);
}

*edit:

The jQuery.post function is an asynchronous javascript call (to get data without a page load).

So when used jQuery.post you can pass parameters to a php script for example and get an answer from it. A short-hand function for this is $.ajax() for example.

With jQuery.post you send 'data' to an 'url' and the 'callbackFunction' is the function that handles the answer. the 'json' in your question is the data type.

In your case this would become something like this:

function firstCallme(postData){
    jQuery.post("url.php", postData, callbackFun(data), "json");
}

callbackFun(successData){
    console.log(successData);
}

jquery.post documentation

where is the post function? – Mohammed H Dec 27 '12 at 12:26 — Mohammed H, Dec 27 '12 at 12:26

Jai · Answer 3 · 2012-12-27T12:31:52.453

0

Try it this way: http://jsfiddle.net/6WxfF/

function firstCallme(iWantToBePassed) {
    callbackFun(iWantToBePassed);
}

function callbackFun(dataFromPostFun) {
    post(dataFromPostFun);
}

function post(callbackFun) {
    jQuery.post('url', 'data', callbackFun, 'json');    
}

$(function() {
    var hel = "Hello";
    firstCallme(hel);
});

edited Dec 27 '12 at 12:31

answered Dec 27 '12 at 12:18

Jai

74,255
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where is the post function? – Mohammed H Dec 27 '12 at 12:27
The function call was already there. I added the function definition later. – Mohammed H Dec 27 '12 at 12:30

score 0 · Answer 4 · answered Dec 27 '12 at 12:24

0

Rewrite post as:

function post(callbackFun, param) {
  jQuery.post('url', 'data', function() { callbackFun(param); }, 'json');    
}

And call it like:

function firstCallme(iWantToBePassed) {
  post(callbackFun, iWantToBePassed);
}

answered Dec 27 '12 at 12:24

techfoobar

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How to pass variable to a callback function

4 Answers4