JavaScript Function Complete Reference

Last Updated : 18 Apr, 2025

A JavaScript function is a set of statements that takes inputs, performs specific computations, and produces outputs. Essentially, a function performs tasks or computations and then returns the result to the user.

Syntax:

function functionName(Parameter1, Parameter2, ..) {
    // Function body
}

Example: Below is a sample program that illustrates the working of functions in JavaScript:

JavaScript

function greetUser(username) {
    console.log(`Hello ${username}, welcome to GeeksforGeeks`);
}
greetUser('Admin');

Output

Hello Admin, welcome to GeeksforGeeks

The Complete List of JavaScript Functions & Properties

JavaScript Function Parameters:

Parameters	Description
Function	The function definition and real values passed to the function in the function definition are known as arguments.
Rest	Improved way to handle function parameters defined, allowing us to more easily handle various inputs as parameters in a function.
Default parameters	In JavaScript, the parameters of functions default to undefined. However, in some situations, it might be useful to set a different default value.

JavaScript Functions Properties:

Properties	Description
length	Return the number of parameters required by a function.
displayName	Set the display name of the function.
caller	Returns the function that invoked the specified function.
name	Return the name of the function.

JavaScript Functions:

Functions	Description
apply()	It is different from the function call() because it takes arguments as an array.
isFinite()	It returns true for all the values except +infinity, -infinity, or NaN.
isNaN()	It returns true if the value is a NaN else returns false.
unescape()	It decodes that string encoded by the escape() function.
escape()	It can be transmitted to any computer in any network which supports ASCII characters.
number()	Convert the data type to a number.
map()	The calling function for each and every array element in an array.
String()	Convert the value of an object to a string value.
eval()	If the argument represents one or more JavaScript statements, eval() evaluates the statements.
uneval()	Create a string representation of the source code of an Object.
parseInt()	Accept the string and radix parameters and convert them into an integer.
parseFloat()	Accept the string and convert it into a floating-point number.
console.log()	To print any kind of variables defined before in it or to just print any message that needs to be displayed to the user.

Basics of Functions:

JavaScript Operations on Function	Description
Function Generator	It needs to generate a value, it does so with the yield keyword rather than return.
Function Binding	In JavaScript, function binding happens using bind() method.
Function Invocation	It is common to use the term “call a function” instead of “invoke a function”.
Function Expression	Create an anonymous function that doesn’t have any function name.
Arrow Functions	Provide generator functions with a concise way to write functions in JavaScript.
Async Function	It checks that we are not breaking the execution thread.
Pure Functions	Returns the same result if the same arguments are passed.
Nested Functions	Return is a combination of the output from the outer as well as the inner function(nested function).

Understanding JavaScript functions is fundamental for effective programming. These functions and properties enable you to write cleaner, more efficient, and reusable code. For more advanced JavaScript tutorials and examples, explore our JavaScript Tutorial and JavaScript Examples.

JavaScript Arrays

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JavaScript Function Complete Reference

The Complete List of JavaScript Functions & Properties

JavaScript Function Parameters:

JavaScript Functions Properties:

JavaScript Functions:

Basics of Functions:

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