JavaScript Tutorial
4. Functions
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A JavaScript
function is a block of JavaScript code that can be executed as a discrete unit.
It involves a function statement along the lines of e.g.:
function func() {
document.getElementById("element").innerHTML
= "Hello";
}
Function definitions can
include parameters (separated by a comma if more than one parameter), e.g. the
following (if passed a string variable) would allow any text to be inserted in
the relevant element’s innerHTML.
function func2(x) {
document.getElementById("element").innerHTML
= x;
}
Such a function would be
invoked by JavaScript such as func2("Hello
World").
Functions are much like
procedures or subroutines in other programming languages. The code inside the
curly brackets executes when the function is invoked. This can happen when an
event occurs, when the function is called from JavaScript code or sometimes
when it is self-invoked. If a function includes a return
statement then the function will stop executing and will return the value
identified by the function’s return statement. The function (technically, a
special type of object) can be distinguished from the act of invoking it. The () operator invokes the function, e.g.
in the above func refers to the
function object, but func() will
invoke the function itself.
The function parameters
are the names listed in the function definition (i.e. the x in the definition of func2). Function arguments are the
values received by the function (i.e. assigned to the function parameters) when
it is invoked.
Function names can
contain letters, digits, underscores and dollar signs (the same rules as apply
to variable
naming applies to function naming). Wherever a variable can be used, a valid
function call evaluating to the same value can also be used.
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