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How to change the value of a global variable inside a function using JavaScript?

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Sep 15, 2023 pm 12:37 PM

如何使用 JavaScript 更改函数内部全局变量的值？

Both types of variables can be declared in any programming language in the context of their access scope. Local variables and global variables.

Global scope variables - Global scope variables are variables declared globally within a code file and can be accessed by any code block or any function within the file. The scope of these variables is global.

Local Scope Variables - These are variables declared inside a function or a specific block of code and can be accessed or used only within that specific code block and not outside that code block. The scope of these variables is limited to a specific block of code, which is why these variables are locally scoped variables.

In this article, we will learn how to use JavaScript to change the value of a global variable in a code file within a function.

It's very simple to change the value of a global variable within a function using JavaScript. In JavaScript, we can change the value of a global variable in two ways as follows -

Change the value directly.
Use square bracket syntax to change the value.

Let us understand the actual implementation of these methods in detail with the help of code examples.

Change the value directly

In this method, we can directly change the value of the global variable and assign it a value by using the name of the global variable.

grammar

The following syntax will help you understand how to directly access and change the value of global variables -

var global_variable_name = initial_value;
function() {
   global_variable_name = new_value;
}

Let’s see the actual implementation of this method with the help of a JavaScript code example.

algorithm

Step 1 - In the first step, we will add two different input elements to the HTML document, each with a type attribute value of number, to obtain two numeric inputs from users of their choice.
Step 2 - In the next step, we will add a button element to the document and use the onclick event, which accepts a function and calls it when the user clicks the button. p>
Step 3 - In the third step, we will define a JavaScript function and assign it as a value to the onclick event of the button added in the previous step.
Step 4 - In this step, we will get the value entered by the user in the input element and change the value of the global variable using the product of these two values. All these operations are performed within the function declared in the previous step.

Example

The following example will explain to you how to use JavaScript to change the value of a global variable in a function -

<html>
<body>
   <h2 id="Change-the-value-of-a-global-variable-inside-of-a-function-using-JavaScript"> Change the value of a global variable inside of a function using JavaScript </h2>
   <p id = "upper">The initial value that is assigned to the global variable <b>globe is: 8</b></p>
   <p>Enter any two numbers:</p>
   <input type = "number" id = "inp1"> <br> <br>
   <input type = "number" id = "inp2"> <br> <br>
   <button id = "btn" onclick = "changeVal()">click to change the value</button>
   <p id = "result"> </p>
   <script>
      var result = document.getElementById("result");
      var globe = 8;
      function changeVal() {
         var inp1 = document.getElementById("inp1");
         var inp2 = document.getElementById("inp2");
         var num1 = Number(inp1.value);
         var num2 = Number(inp2.value);
         var prevGlobe = globe;
         globe = num1 * num2;
         result.innerHTML += " The value of the global variable <b> globe </b> is changed from <b> " + prevGlobe + " </b> to <b> " + globe + " </b> the product of the two numbers <b> " + num1 + " * " + num2 + " </b> entered by you. <br> ";
      }
   </script>
</body>
</html>

In the above example, we can clearly see that we change the value of the global variable globe from 8 to the value of the global variable globe by the user every time in the named

changeVal ()

within the function.

Square bracket syntax for changing values

This is another way or syntax to change the value of a global variable within a function using JavaScript. In this method, instead of accessing the variable directly, we will use square bracket syntax to access and change its value.

grammar

The following syntax will show you how to use square bracket syntax to access and change the value of global variables -

var global_variable = initial_value;
function() {
   window['global_variable'] = new_value; 
}

Let's actually implement this method and try changing the value of the global variable in the code example.

algorithm

The algorithm for this example is similar to the algorithm for the previous example. You just need to change the syntax for accessing variables inside the function from direct syntax to square bracket syntax. The examples below will help you understand in detail the changes you must make.

Example

The following example will show you how to use square bracket syntax to access and change the value of the global syntax -

<html>
<body>
   <h2 id="Change-the-value-of-a-global-variable-inside-of-a-function-using-JavaScript">Change the value of a global variable inside of a function using JavaScript</h2>
   <p id = "upper">The initial value that is assigned to the global variable <b>globe is: 8</b></p>
   <p>Enter any two numbers:</p>
   <input type = "number" id = "inp1"> <br> <br>
   <input type = "number" id = "inp2"> <br> <br>
   <button id = "btn" onclick = "changeVal()">click to change the value</button>
   <p id = "result"> </p>
   <script>
      var result = document.getElementById("result");
      var globe = 8;
      function changeVal() {
         var inp1 = document.getElementById("inp1");
         var inp2 = document.getElementById("inp2");
         var num1 = Number(inp1.value);
         var num2 = Number(inp2.value);
         var prevGlobe = window['globe'];
         window['globe'] = num1 * num2;
         result.innerHTML += " The value of the global variable <b> globe </b> is changed from <b> " + prevGlobe + " </b> to <b> " + globe + " </b> the product of the two numbers <b> " + num1 + " * " + num2 + " </b> entered by you. <br> ";
      }
   </script>
</body>
</html>

In this example, we use square bracket syntax to access the value of the global variable

globe

and change it from its initial value to the product of two input numbers.

###In this article, we learned about two different ways to change the value of a global variable from its initial value to some new value. We discuss both methods in detail with code examples for each method to understand their practical implementation. ###

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