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JavaScript Function Complete Reference

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  • Difficulty Level : Easy
  • Last Updated : 17 Mar, 2023
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The JavaScript function is a set of statements that take inputs, do some specific computation, and produce output. Basically, a function is a set of statements that performs some tasks or does some computation and then return the result to the user.


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

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


<script type = "text/javascript">
    // Function definition
    function welcomeMsg(name) {
    console.log("Hello " + name +" welcome to GeeksforGeeks");
    // creating a variable
    var nameVal = "Admin";
    // calling the function


Hello Admin welcome to GeeksforGeeks

The Complete List of JavaScript Functions & Properties is listed below:

JavaScript Function Parameters:



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:



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:



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


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).

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