04-functions.md

11.13 Built-in Functions

A function is a piece of code that performs some operations on variables to fulfill a specific task. It takes one or more input values, processes them, and returns an output value. JavaScript provides built-in functions that are already defined to fulfill a certain task. Table 11.5 lists the built-in functions.

Function	Description	Example
alert()	Displays a dialog box with some information and OK button	alert("Please fill all fields of the form"); Displays a message box with the instruction
confirm()	Displays a dialog box with OK and Cancel buttons. It verifies an action, which a user wants to perform	confirm("Are you sure you want to close the page?"); Displays a message box with the question
parseInt()	Converts a string value into a numeric value	parseInt("25 years");
parseFloat()	Converts a string value into a number with decimal point	parseFloat("10.33"); Returns 10.33
eval()	Evaluates an expression and returns the evaluated result	eval("2+2"); Returns 4
isNaN	Checks whether a value is not a number	isNaN("Hello"); Returns true
prompt()	Displays a dialog box that accepts an input value through a text box. It also accepts default value for text box.	prompt("Enter your name", "Name"); Displays message in dialog box and Name in text box.

NOTE - The \n character, when used in the alert() function, prints the information on a new line. This does not happen when the \n character is used with the write methods of the document object.