A function is a block of code which will execute whenever it is
called. To become a good JavaScript programmer understanding functions are the
key.
In JavaScript functions are declared with function keyword. It is
possible to create named functions, anonymous functions / lambda functions,
self invoking functions. You can pass parameters to functions; these parameters
can be any JavaScript type.
// named function
function myfun(){
document.write(“this
is simple named function”);
}
// named function with
params
function myfun (name,age){
document.write(“My
name is “ + name, “ I am “ + age);
}
To call a function we have to use () operator. In the above
example myfun is the function name so you can call function like below.
//invoking a named function
myfun();
All the declared parameters are local variables to the functions.
You can omit declared parameters; misplace the order of parameters, mismatch
data types when calling a function, it is perfectly legal in JavaScript.
//ignored age param
myfun("srinivas");
// prints srinivas
//params are local
varibles to the function
function
myfun(name,age){
name = "srinivas";
name = "srinivas";
age = 23;
document.write(name," " + age);
}
myfun("something", 25); // prints srinivas 23
Functions are objects
in the JavaScript. so you can pass them as parameters and can assign to the
variable.
// creating a
anonymous function and assigning them to a variable
var printNameAge =
function(name,age){
document.write(name,"
" + age);
}
// whenever you need
to call this anonymous function need to call like below
printNameAge('srinivas',23);
// prints srinivas 23
Variables / parameters
declared in the functions are private variables. If you want to make them as public
use ‘this’ keyword.
//using the this key
word
function
myfun(name,age){
this.name =
"srinivas";
this.age = 23;
document.write(name,"
" + age);
}
myfun("something",
25); // prints something 25
Self invoking function
is a function which will invoke itself. by using these we can create some
utility functions and modules. These are very helpful to make the global space
clean and avoid name space collisions.
// simple self
invoking function
(function(){alert('hi')})();
Summary
- Functions are declared with the function key word, every function has a body with some statements.
- Functions will be executed with the () operators.
- Functions may or may not have parameters
- It is perfectly legal omitting some of the parameters, passing them in a different order, passing different types.
- Functions can be named functions, anonymous functions, self invoked functions
- Function parameters are local variables to the functions
- By default declared variables in the function are private, to make them as public use ‘this’ keyword.
