JavaScript functions

A function is a series of commands that performs an action or computes a value. A function consists of the function name, which identifies it; parameters, which are values used by the function; and a series of commands that are run when the functions is called. Not all functions require parameters. The general syntax of a JavaScript function is:

function function_name(parameters) { JavaScript commands }

Example of a function performing an action is given below. This function takes two parameters par1 and par2 and creates a table row consisting of two columns containing these parameters:

function tabRow(par1, par2) { document.write("<tr><td>" + par1 + </td> + "<td>" + par2 + "</td></tr>"); }

Try how it works:

par1:
par2:

The following function takes a number as a parameter, and computes the area of a disk of that radius. The function uses the constant PI (=3.1415...), which is a part of the Math object:

function computeArea(radius) { return Math.PI * radius * radius; }

Try how it works:

radius:

The Math object offers a plenty of useful methods, some of them are listed below. Try how they work.

JavaScript code	Comments	Results
Enter x:	enter a value of x for testing
`Math.abs(x)`	returns the absolute value of x
`Math.sin(x)`	returns the sine of x
`Math.cos(x)`	returns the cosine of x
`Math.round(x)`	rounds x to the nearest integer
`Math.ceil(x)`	rounds x up to the next highest integer
`Math.floor(x)`	rounds x to the next lowest integer
`Math.random()`	returns a random number between 0 and 1

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JavaScript functions