java script function

Functions are one of the fundamental building blocks in JavaScript. A function in JavaScript is similar to a procedure—a set of statements that performs a task or calculates a value, but for a procedure to qualify as a function, it should take some input and return an output where there is some obvious relationship between the input and the output. To use a function, you must define it somewhere in the scope from which you wish to call it

Defining functions

There are two type of defining the function

• Function declaration which contain

1 - The name of the function.

2- A list of parameters to the function, enclosed in parentheses and separated by commas.

3- The JavaScript statements that define the function, enclosed in curly brackets, {…}. For example

function square(number) {

return number * number;

}

• Function expressions

While the function declaration above is syntactically a statement, functions can also be created by a function expression.

For example, the function square could have been defined as:

square = function(number) {

return number * number 

}

** Function expressions are convenient when passing a function as an argument to another function. The following example shows a map function that should receive a function as first argument and an array as second argument.**

** Calling functions **

Defining a function does not execute it. Defining it names the function and specifies what to do when the function is called.