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JavaScript var Keyword | Declare a Global Variable
The JavaScript var keyword is used to declare a global variable, that can be updated as well as re-declared. For example:
HTML with JavaScript Code
<!DOCTYPE html> <html> <body> <script> var x = "codescracker.com"; document.write("1. ", x, "<BR>"); function myFun() { document.write("2. ", x, "<BR>"); x = "codes cracker"; document.write("3. ", x, "<BR>"); } myFun(); document.write("4. ", x, "<BR>"); var x = "JavaScript is Fun!"; document.write(x); </script> </body> </html>
Output
Note - The default value of variable, declared using the var keyword, is undefined. Therefore, accessing a var variable without its initialization, returns or prints undefined. For example:
HTML with JavaScript Code
<!DOCTYPE html> <html> <body> <script> var a; document.write(a); </script> </body> </html>
Output
JavaScript var Syntax
The syntax of var keyword in JavaScript, is:
var variableName = variableValue;
The variableValue is optional. That is, we can assign the value either at the time of declaration, or later. For example:
HTML with JavaScript Code
<!DOCTYPE html> <html> <body> <p>The sum of 10 and 20 is <span id="x"></span></p> <script> var a = 10; var b = 20; var sum; sum = a + b; document.getElementById("x").innerHTML = sum; </script> </body> </html>
Output
The sum of 10 and 20 is
As you can see from the above example, the variable a and b are initialized at the time of its declaration. Whereas the variable sum is initialized later, after the declaration.
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