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Trigger function only on "onclick"

Hello I need a function to run when an a tag is clicked. I am using the onclick="" but it seems that the function runs on page load, instead of waiting to run when the a tag is clicked on. How do I make it so the function only runs when the a tag is clicked?
Here is my code.
HTML:
<a class="req_btn" onclick="conversionOne()">text</a>
<script type='text/javascript'>
(function conversionOne() {
alert("something");
})();
</script>
Thanks!

You are invoking the function when the script loads using an IIFE. Instead of this:
(function conversionOne() {
alert("something");
})();
Do this:
function conversionOne() {
alert("something");
}

You are using a self-executing function.
Declare the function in the global scope without executing it.
function conversionOne() {
alert("something");
}

Doing this
(function(){
/** code **/
})();
Means the code will be executed imediatelly.
in your case you want to create a function so you need this :
function conversionOne() {
/** code **/
}
or
var conversionOne = function () {
/** code **/
}

(function conversionOne() {
alert("something");
})();
calling function like this will work onload
Change this to
function conversionOne() {
alert("something");
};
More info

jQuery : Object has no method for $.fn

i have this function in my js file
(function($) {
$.fn.foobar = function() {
// some code
};
})(jQuery);
and when i call the following
jQuery(function() {
$.getScript("http://ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min.js");
$.getScript("http://ajax.googleapis.com/ajax/libs/jqueryui/1.10.3/jquery-ui.min.js");
jQuery('object').foobar();
});
it gives me the following
Uncaught TypeError: Object [object Object] has no method 'foobar'
i'm trying this on Rails file (*.js.erb)

I guess you are overwriting your jQuery array with that second one, try doing this:
(function($) {
$.fn.foobar = function() {
console.log(true);
};
})(jQuery);
(function($) {
$.getScript("http://ajax.googleapis.com/ajax/libs/jquery/1.10.2/jquery.min.js", function() {
$('body').foobar();
});
})(jQuery);
working fiddle

Only run these codes in the fiddle, it runs fine. So, i guess that your code may be have some error at other place.I suggest you show more code for the question.

try something like this
<script src="jquery.js">
<script>
(function($) {
$.fn.foobar = function() {
// some code
};
})(jQuery);
$(function(){
jQuery('object').foobar();
})
</script>

Very simple jquery custom function throws error

I have the following code:
$(document).ready(function() {
$.fn.addRemoveButton = function() {
alert(1);
};
$.addRemoveButton();
});
And I get the following error message from firebug:
TypeError: $.addRemoveButton is not a function
$.addRemoveButton();
Why and how can I fix this?

You need to define a selector, try this:
$(document).ready(function() {
$.fn.addRemoveButton = function() {
alert(1);
};
$(document).addRemoveButton();
});
Here is working jsFiddle.

You need to apply that to any DOM.
Example
jQuery Code
$(function()
{
$.fn.addRemoveButton = function() {
alert(1);
};
$('#letit').addRemoveButton();
});
HTML Code
<div id="letit"></div>

or, you can create it as a jQuery global function:
$(document).ready(function() {
$.addRemoveButton = function() { // removed the .fn
alert(1);
};
$.addRemoveButton();
});
This binds the function to the jQuery object, where you can then use it like in your original example.
See this post for the difference between jQuery.fn.method and jQuery.method

jsLint shows "somefunction() was used before it was defined" error

I am new to jQuery and I am using jsLint on jsFiddle to test if I have errors on my code snippets. Below is the structure of the code I am using but jsLint shows that my function expandToggle() was used before it was defined:
$(document).ready(function() {
expandToggle();
});
function expandToggle() {
//dosomething
}
Can someone help me what this error means?

It means what it says. To make jsLint calm down switch your code around.
function expandToggle() {
//dosomething
}
$(document).ready(function() {
expandToggle();
});

as the error states , define the function first
function expandToggle() {
//dosomething
}
then use it
$(document).ready(function() {
expandToggle();
});

It means this:
$(document).ready(function() {
expandToggle(); });
Was before this:
function expandToggle() {
//dosomething }
To fix just rearrange them:
function expandToggle() {
//dosomething }
$(document).ready(function() {
expandToggle(); });

calling Jquery function from javascript

How can i call a jQuery function from javascript?
//jquery
$(function() {
function my_fun(){
/.. some operations ../
}
});
//just js
function js_fun () {
my_fun(); //== call jquery function
}

Yes you can (this is how I understand the original question).
Here is how I did it. Just tie it into outside context.
For example:
//javascript
my_function = null;
//jquery
$(function() {
function my_fun(){
/.. some operations ../
}
my_function = my_fun;
})
//just js
function js_fun () {
my_function(); //== call jquery function - just Reference is globally defined not function itself
}
I encountered this same problem when trying to access methods of the object, that was instantiated
on DOM object ready only. Works. My example:
MyControl.prototype = {
init: function {
// init something
}
update: function () {
// something useful, like updating the list items of control or etc.
}
}
MyCtrl = null;
// create jquery plug-in
$.fn.aControl = function () {
var control = new MyControl(this);
control.init();
MyCtrl = control; // here is the trick
return control;
}
now you can use something simple like:
function() = {
MyCtrl.update(); // yes!
}

You can't.
function(){
function my_fun(){
/.. some operations ../
}
}
That is a closure. my_fun() is defined only inside of that anonymous function. You can only call my_fun() if you declare it at the correct level of scope, i.e., globally.
$(function () {/* something */}) is an IIFE, meaning it executes immediately when the DOM is ready. By declaring my_fun() inside of that anonymous function, you prevent the rest of the script from "seeing" it.
Of course, if you want to run this function when the DOM has fully loaded, you should do the following:
function my_fun(){
/* some operations */
}
$(function(){
my_fun(); //run my_fun() ondomready
});
// just js
function js_fun(){
my_fun(); //== call my_fun() again
}

var jqueryFunction;
$().ready(function(){
//jQuery function
jqueryFunction = function( _msg )
{
alert( _msg );
}
})
//javascript function
function jsFunction()
{
//Invoke jQuery Function
jqueryFunction("Call from js to jQuery");
}
http://www.designscripting.com/2012/08/call-jquery-function-from-javascript/

<script>
// Instantiate your javascript function
niceJavascriptRoutine = null;
// Begin jQuery
$(document).ready(function() {
// Your jQuery function
function niceJqueryRoutine() {
// some code
}
// Point the javascript function to the jQuery function
niceJavaScriptRoutine = niceJueryRoutine;
});
</script>

jQuery functions are called just like JavaScript functions.
For example, to dynamically add the class "red" to the document element with the id "orderedlist" using the jQuery addClass function:
$("#orderedlist").addClass("red");
As opposed to a regular line of JavaScript calling a regular function:
var x = document.getElementById("orderedlist");
addClass() is a jQuery function, getElementById() is a JavaScript function.
The dollar sign function makes the jQuery addClass function available.
The only difference is the jQuery example is calling the addclass function of the jQuery object $("#orderedlist") and the regular example is calling a function of the document object.
In your code
$(function() {
// code to execute when the DOM is ready
});
Is used to specify code to run when the DOM is ready.
It does not differentiate (as you may think) what is "jQuery code" from regular JavaScript code.
So, to answer your question, just call functions you defined as you normally would.
//create a function
function my_fun(){
// call a jQuery function:
$("#orderedlist").addClass("red");
}
//call the function you defined:
myfun();

I made it...
I just write
jQuery('#container').append(html)
instead
document.getElementById('container').innerHTML += html;

//javascript function calling an jquery function
//In javascript part
function js_show_score()
{
//we use so many javascript library, So please use 'jQuery' avoid '$'
jQuery(function(){
//Call any jquery function
show_score(); //jquery function
});(jQuery);
}
//In Jquery part
jQuery(function(){
//Jq Score function
function show_score()
{
$('#score').val("10");
}
});(jQuery);

My problem was that I was looking at it from the long angle:
function new_line() {
var html= '<div><br><input type="text" value="" id="dateP_'+ i +'"></div>';
document.getElementById("container").innerHTML += html;
$('#dateP_'+i).datepicker({
showOn: 'button',
buttonImage: 'calendar.gif',
buttonImageOnly: true
});
i++;
}

<script>
$.myjQuery = function() {
alert("jQuery");
};
$(document).ready(function() {
alert("Welcome!");
});
function display() {
$.myjQuery();
};
</script>
<input type="button" value="submit" onclick=" display();">
Hope this will work for you!