How to change the value of a global variable inside of a function using JavaScript ? Last Updated : 13 Apr, 2023 Comments Improve Suggest changes Like Article Like Report Pre-requisite: Global and Local variables in JavaScript Local Scope: Variables that are declared inside a function is called local variables and these are accessed only inside the function. Local variables are deleted when the function is completed. Global Scope: Global variables can be accessed from inside and outside the function. They are deleted when the browser window is closed but are available to other pages loaded on the same window. There are two ways to declare a variable globally: Declare a variable outside the functions.Assign a value to a variable inside a function without declaring it using the "var" keyword. Example: In this example, we will define global variables with user input and manipulate them from inside the function HTML <body> <h1 style="color:green"> GeeksForGeeks </h1> <b>Enter first number :- </b> <input type="number" id="fNum"> <br><br> <b>Enter second number :- </b> <input type="number" id="sNum"> <br><br> <button onclick="add()">Add</button> <button onclick="subtract()">Subtract</button> <p id="result" style="color:green; font-weight:bold;"> </p> <script> // Declare global variables var globalFirstNum1 = 9; var globalSecondNum1 = 8; function add() { // Access and change globalFirstNum1 and globalSecondNum1 globalFirstNum1 = Number(document.getElementById("fNum").value); globalSecondNum1 = Number(document.getElementById("sNum").value); // Add local variables var result = globalFirstNum1 + globalSecondNum1; var output = "Sum of 2 numbers is " + result; // Display result document.getElementById("result").innerHTML = output; } // Declare global variables globalFirstNum2 = 8; globalSecondNum2 = 9; function subtract() { // Access and change globalFirstNum2 // and globalSecondNum2 globalFirstNum2 = Number(document.getElementById("fNum").value); globalSecondNum2 = Number(document.getElementById("sNum").value); // Use global variables to subtract numbers var result = globalFirstNum2 - globalSecondNum2; var output = "Difference of 2 numbers is " + result; document.getElementById("result").innerHTML = output; } </script> </body> Output: Comment More infoAdvertise with us Next Article How to change the value of a global variable inside of a function using JavaScript ? A AshaRamMeena Follow Improve Article Tags : JavaScript Web Technologies javascript-functions JavaScript-Questions Similar Reads How to declare the optional function parameters in JavaScript ? Declaring optional function parameters in JavaScript means defining function parameters that aren't required when the function is called. You can assign default values to these parameters using the = syntax, so if no argument is provided, the default value is used instead. These are the following ap 3 min read How to get the javascript function parameter names/values dynamically ? In this article, we are given any arbitrary JavaScript function and the task is to return the parameter names of the function. Approach: JavaScript contains a method called toString() which is used to represent a function code in its string representation. This method is used to get the parameter na 2 min read How To Include a JavaScript File in Another JavaScript File? 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