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How to use an external function in event handler in JQuery

I want to do something like this:
$(div).bind('click', myFunctionWithManyManyLinesOfCode(param) );
.....
function myFunctionWithManyManyLinesOfCode(args){
//50 lines of Code
}
If I do this the function is executed when the code reaches the point and doesn't execute on clicks.
If I include the code from the function myFunctionWithManyManyLinesOfCode in the bind method it will be a mess of code.
Also, I've tried this, but I cannot reference variables, they are undefined
$(div).bind('click', function() {myFunctionWithManyManyLinesOfCode(param)} );

You can pass whatever data you want to in the following way.
This should do the trick for you. If something is unclear please write a comment.
Edit: As stated in the comments you should use on and not bind.
function myFunction(e){
console.log(e.data.id);
}
$('#example').on('click',{id: "WHATEVER"}, myFunction);
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<button id="example">Test</button>

First of all, 50 lines of code are too much for one function and should be divided into smaller methods, but you can use this method:
var hello = () => {
alert(123)
}
$("p").click(hello);

How do I use a function as a variable in JavaScript?

I want to be able to put the code in one place and call it from several different events.
Currently I have a selector and an event:
$("input[type='checkbox']").on('click', function () {
// code works here //
});
I use the same code elsewhere in the file, however using a different selector.
$(".product_table").on('change', '.edit_quantity', function () {
// code works here //
});
I have tried following the advice given elsewhere on StackOverflow, to simply give my function a name and then call the named function but that is not working for me. The code simply does not run.
$(".product_table").on('change', '.edit_quantity', function () {
calculateTotals() {
// code does not work //
}
});
So, I tried putting the code into it's own function separate from the event and call it inside the event, and that is not working for me as well.
calculateTotals() {
// code does not work //
}
So what am I doing wrong ?

You could pass your function as a variable.
You want to add listeners for events after the DOM has loaded, JQuery helps with $(document).ready(fn); (ref).
To fix your code:
$(document).ready(function() {
$("input[type='checkbox']").on('click', calculateTotalsEvent)
$(".product_table").on('change', '.edit_quantity', calculateTotalsEvent)
});
function calculateTotalsEvent(evt) {
//do something
alert('fired');
}
Update:
Vince asked:
This worked for me - thank you, however one question: you say, "pass your function as a variable" ... I don't see where you are doing this. Can you explain ? tks. – Vince
Response:
In JavaScript you can assign functions to variables.
You probably do this all the time when doing:
function hello() {
//
}
You define window.hello.
You are adding to Global Namespace.
JavaScript window object
This generally leads to ambiguous JavaScript architecture/spaghetti code.
I organise with a Namespace Structure.
A small example of this would be:
app.js
var app = {
controllers: {}
};
You are defining window.app (just a json object) with a key of controllers with a value of an object.
something-ctlr.js
app.controllers.somethingCtlr.eventName = function(evt) {
//evt.preventDefault?
//check origin of evt? switch? throw if no evt? test using instanceof?
alert('hi');
}
You are defining a new key on the previously defined app.controllers.somethingCtlrcalled eventName.
You can invoke the function with ();.
app.controllers.somethingCtlr.eventName();
This will go to the key in the object, and then invoke it.
You can pass the function as a variable like so.
anotherFunction(app.controllers.somethingCtlr.eventName);
You can then invoke it in the function like so
function anotherFunction(someFn) { someFn();}
The javascript files would be structured like so:
+-html
+-stylesheets
+-javascript-+
+-app-+
+-app.js
+-controllers-+
+-something-ctlr.js
Invoke via chrome developer tools with:
app.controllers.somethingCtlr.eventName();
You can pass it as a variable like so:
$(document).ready(function() {
$('button').click(app.controllers.somethingCtlr.eventName);
});
JQuery (ref).
I hope this helps,
Rhys

It looks like you were on the right track but had some incorrect syntax. No need for { } when calling a function. This code should behave properly once you add code inside of the calculateTotals function.
$(".product_table").on('change', '.edit_quantity', function () {
calculateTotals();
});
$("input[type='checkbox']").on('click',function() {
calculateTotals();
});
function calculateTotals() {
//your code...
}

You could just condense it all into a single function. The onchange event works for both the check box and the text input (no need for a click handler). And jQuery allows you to add multiple selectors.
$('input[type=checkbox], .product_table .edit_quantity').on('change', function() {
console.log('do some calculation...');
});
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
<div class="product_table">
<input type="checkbox">
<input class="edit_quantity">
</div>

Call function defined inside $(document).ready()

In and external JS file I have
$(document).ready(function() {
var example = function(){ alert("hello") }
});
and I want to call that function from my html, how would I do that?
<img src="..." ondblclick="example()" />
n.b. I'm aware of jquery dblclick() but curious about how to correctly do the above.

$(document).ready(function() {
window.example = function() {
alert("hello")
}
});
Or define it outside, if possible. It doesn't look like it has to be defined inside document ready at all.

The other solutions here will work, but structurally in your project, the best solution is to remove the event handling code from the HTML and hook up the event entirely via javascript (separate the HTML/JS). Since you already have jQuery in your project, this is very easy. To do that, all you need to do is to put some sort of identification on the image:
<img id="example" src="..." />
Then, in you can just hook up the event code in your ready() function like this
$(document).ready(function() {
$("#example").dblclick(function() {
alert("Hello");
});
});
This has the following advantages:
It creates no global variables - reducing the global namespace pollution.
It separates the HTML from the javascript which keeps all code governing the behavior in one compact spot and is usually a good thing
Using event listeners is a bit more scalable than using .ondblclick - allowing multiple different parts of code to use non-conflicting event handlers on the same object

Your function should be global (in fact, property of window object) if you want to access it from HTML. But best practice is to avoid global variables and functions, using namespace instead:
// let's publish our namespace to window object
if (!window.myNamespace){
// creating an empty global object
var myNamespace = {};
}
// and add our function to it
$(document).ready(function() {
myNamespace.example = function(){ alert("hello"); }
});
We can use it in HTML like this:
<img src="..." ondblclick="myNamespace.example()" />

The best option would be to simply define the function outside document.ready(). There is no reason defining the function within the $(document).ready() event is necessary, as if you call the function within the $(document).ready() function, the document is guarenteed to be ready.
However, you can also define the function on the global window object, like so:
$(document).ready(function() {
window.example = function(){ alert("hello") }
});

You can either move the function declaration outside of the DOM-ready handler:
function example(){ alert("hello") }
$(document).ready(function() {
// code
});
But the better solution is to keep JavaScript in your .js files and avoid the inline event handlers. Give your element an id and fetch it:
<img src="..." id="imgid" />
$(document).ready(function() {
document.getElementById("imgid").ondblclick = function(){ alert("hello") }
});

#Esailija has answered it correctly but if you want to keep it as it is then simply remove var and make it global.
var example;
$(document).ready(function() {
example = function() {
alert("hello")
}
});
If you do not put var the variable/function/object becomes global. Using var you were setting its context within document.ready function.

Scope issue inside a custom object

I think I am having a scope visibility issue I can't figure out exactly: when I log the variable displayatonce I get back the right result, but as I try to use the buttons I get nothing in return. I have also tried to log this.navbuttons but all I get is an empty set... I really don't get what's wrong with this code.
<!-- html code -->
<div id="nav">
Previous
Next
</div>
/* Js Script with jQuery */
(function() {
var NewsNavigator = {
init: function(config) {
this.navbuttons = config.navbuttons;
this.displayatonce = config.displayatonce;
this.counter = 0;
this.showNews();
this.enableNav();
},
showNews: function() {
console.log(this.displayatonce);
},
enableNav: function() {
console.log(this.navbuttons);
this.navbuttons.on('click', function() {
console.log("clicked");
});
}
};
NewsNavigator.init({
displayatonce: 3,
navbuttons: $('div#nav').find('a')
});
})();

That is happening because as you are using (function())(); which executes the function immediately, maybe it's running the code before the dom is ready
everything is working fine in the below demo
DEMO
Put all your code inside document ready or at least call the initialize method inside doc ready block like
$(function(){
NewsNavigator.init({
displayatonce: 3,
navbuttons: $('div#nav').find('a')
});
});
Read more about Javascript self executing Anonymous function here
Javascript self executing function "is not a function"
or
http://markdalgleish.com/2011/03/self-executing-anonymous-functions/

You're using jQuery too soon, specifically before the DOM is ready to be searched.
Here is fiddle demonstrating this: http://jsfiddle.net/w7KaY/ (JavaScript is placed in <head>, so init() is invoked pretty early) while here (http://jsfiddle.net/w7KaY/1/), the call to init() is encapsulated in an event handler for jQuery's DOM-ready event.

Make sure the html elements are there in the DOM. I don't see any issue with the script other than the fact you have to use the bind method for binding to events.
this.navbuttons.bind('click', function() {
console.log("clicked");
});

Jquery and javascript namepsace

In trying to namespace my js/jquery code, I have come up against the following problem.
Basically, I used to write all my JS code in each html/php file, and I want to abstract that away to a single js file with namespaces.
So, in my html file I have:
<script type="text/javascript">
$(document).ready(productActions.init());
</script>
And in my js file I have:
var productActions = {
init: function() {
alert('initialsed');
$('#field_id').change(function() {
alert('ok!');
});
}
The productActions init function is definitely running, because I get the first alert (initialised). However, it seems that none of the jquery binding functions do anything at all. Stepping through the init function shows that the above change function is being registered, but actually changing the value in the field does absolutely nothing.
Am I missing something obvious here?

$(document).ready(productActions.init());
This code calls init() immediately and passes its return value to ready(...). (just like any other function call)
Instead, you can write
$(document).ready(productActions.init);
To pass the function itself. Howeverm this will call it with the wrong this; if you need this, write
$(document).ready(function() { productActions.init() });