The concepts presented here discuss functions as an executable code unit that can be assigned and reused. You are expected to know the general purpose of a function and how to use it. If you have written any code before, you most likely know how to create and use a function.

In JavaFX, A function is a specialized code block preceded by the function keyword. It can accept zero or more typed parameters and always returns a typed value. Here is the declaration of a function type assigned to variable called squareIt, which returns the squared value of the number passed in as parameter. Complete code listing can be found at ch01/source-code/src/javafx/SimpleFunction.fx.

var squareIt : function(:Number):Number;
squareIt = function (x) {
x * x;
}
var square3 = squareIt(3);
println ("3 squared = {square3}");

In JavaFX, a function has a distinct, definable type (similar to String, Number, and Integer). A function type is defined by its parameter signature and its return type. Variables (and parameters) can be assigned a function type. For instance, in the previous snippet, variable squareIt is declared as being a function type. This means that the variable squareIt can be assigned a function that takes one parameter of type Number and returns a value of type Number. squareIt can be used anywhere a function call can be used, as shown in the call var square3 = squareIt(3).

Note that the declaration and definition of the function can be combined in one step, as show next:

function squareIt(x:Number):Number{
x * x;
}

The JavaFX compiler can infer the types associated with a function's parameter signature and return value. Therefore, the function definition can be reduced to:

function squareIt(x) {
x*x;
}

The type inference engine in JavaFX will determine the proper type of the parameter based on value of the parameter at runtime. The return type of the function is based on the type of the last statement in the function or the type of the value used in the return statement.

There are couple more features about functions in which you may be interested.

var f = 10;
bound function increaseIt(a:Number):Number {
a + f;
}
var x = 5;
def y = bind increaseIt(x);

function run() {
println ("I am always called!");
}