My programing background is that I learned a little Java in school. JavaScript syntax tends to confuse me for some reason. The JavaScript code below is a pattern of syntax that I don't know what to make of:
foo.ready = function(variable){... var whatever = variable.bar();
One of my main points of confusion is the parameter. For a contrasting example, in Java, if I call a method with one parameter, the call sends one parameter. I don't see how the parameter named 'variable' is ever set.
The variable is assigned when foo.ready is invoked, and passed some value (presumably a function).
var foo = {}; // 1. Create an object named "foo"
// 2. Assign a function to the "ready" property of "foo"
foo.ready = function(variable) {
// 4. "foo.ready" has been invoked, and received a function to its
// "variable" parameter, which it then invokes.
// The return value is assigned to "whatever"
var whatever = variable();
alert( whatever ); // 5. alert the value returned from the function
};
// 3. Invoke "foo.ready" passing a function as the argument.
// The function merely returns a string
foo.ready( function() { return "Hello world"; } );
Here's a working example: http://jsfiddle.net/69grz/
variable can be much more than a real variable, it can also be a function or a handler/object. In this case you call the function bar() on the object variable
foo.ready refers to an entire function. You can call foo.ready(), with any number of arguments, too. This is a typical call-back pattern: Whoever is in charge of the foo object wants to call you back when she's ready, so you pass this function to her.
You can't really control how many variables (of any type!) will be passed to your function, but presumably the documentation will have told you that you'll receive at least one.
Here is some code that makes that work:
// foo is an object
var foo = {};
// Create a function and assign to the ready property
foo.ready = function(variable){
var whatever = variable.bar();
};
// Create an object that contains a function named bar
var x = {
bar: function(){ return 42; }
};
// Call the function in foo with the object as parameter
foo.ready(x);
The expression variable.bar() will call the function in the object x which returns the value 42, which is then assigned to the variable whatever.
variableis not set in that code. What's the complete code look like?