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JavaScript Function Complete Reference

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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.

Syntax:

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

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

Javascript

// Function definition
function welcomeMsg(name) {
    console.log("Hello " + name 
        + " welcome to GeeksforGeeks");
}
  
// creating a variable
let nameVal = "Admin";
  
// calling the function
welcomeMsg(nameVal);

                    

Output:

Hello Admin welcome to GeeksforGeeks

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

JavaScript Function Parameters:

 Parameters

Description

Example

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

Properties

Description

Example

length Return the number of parameters required by a function.
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displayNameSet the display name of the function.
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caller Returns the function that invoked the specified function.
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nameReturn the name of the function.
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JavaScript Functions:

 Functions

Description

Example

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

JavaScript Operations on Function

Description

Example

Function GeneratorIt needs to generate a value, it does so with the yield keyword rather than return. 
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Function BindingIn JavaScript, function binding happens using bind() method. 
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Function InvocationIt is common to use the term “call a function” instead of “invoke a function”. 
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Function ExpressionCreate an anonymous function that doesn’t have any function name. 
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Arrow FunctionsProvide generator functions with a concise way to write functions in JavaScript. 
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Async FunctionIt checks that we are not breaking the execution thread.
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Pure FunctionsReturns the same result if the same arguments are passed.
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Nested FunctionsReturn is a combination of the output from the outer as well as the inner function(nested function).
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Last Updated : 24 May, 2023
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