Functions in JavaScript bring out the real flexibility of the language. Functions can be stored in variables, defined at runtime. Even inbuilt functions can be redefined.
Declaring functions
function add(a,b)
{
return a+b;
}
a and b are the 2 parameters. I can call this function in the following way
add(3,4). a will become 3, and b will be 4. Answer will be 7.
What happens if I pass only one parameter. add(3).a will be 3, b will be undefined. Answer will be NaN.
Parameters Array
JavaScript creates an array of all parameters passed to a function. This can be used to access all parameters no matter how many are passed.
Consider the following example:
function add() {
var sum = 0;
for (var i = 0; i <= arguments.length – 1; i++)
sum = sum + arguments[i];
return sum;
}
Now, we can call this function as add(1,2,3,4). This will create an array arguments with the values {1,2,3,4}. The answer will be 10.
We can define a function and store it in a variable and then call it.
var x = function () {
var sum = 0;
for (var i = 0; i <= arguments.length – 1; i++)
sum = sum + arguments[i];
return sum;
};
var result = x(1,2,3,4); Answer 10.
Replacing x by the definition we get an anonymous function.
var result = function () {
var sum = 0;
for (var i = 0; i <= arguments.length – 1; i++)
sum = sum + arguments[i];
return sum;
}(1,2,3,4) ;
Answer is 10.
Finally, we can redefine the in built JavaScript functions as well.
For example the prompt function shows a message box with a textbox.
I can redefine the prompt function as
prompt = function () {
var sum = 0;
for (var i = 0; i <= arguments.length – 1; i++)
sum = sum + arguments[i];
return sum;
}
var result = prompt(1, 2, 3, 4);
Answer =10;
We can even redefine functions inside objects.
Thus the following will redefine Math.sqrt.
Math.sqrt = function () {
var sum = 0;
for (var i = 0; i <= arguments.length – 1; i++)
sum = sum + arguments[i];
return sum;
}
var result = Math.sqrt(1, 2, 3, 4); Answer will be 10 like before.
JavaScript is incredibly flexible. Unleash your creativity and enjoy.
