A JavaScript variable is a named storage location for data. There are two main types of variables in JavaScript: local variables and global variables.
1. Name must start with a letter (a to z or A to Z), underscore (_), or dollar ($) sign.
2. After the first letter, you can use digits (0 to 9), for example, value1.
3. JavaScript variables are case sensitive; for example, x and X are different variables.
var x = 10;
var _value = "javascript";
var 123 = 30; // Error: variable name cannot start with a digit
var *a = 32; // Error: variable name cannot start with an asterisk
<!DOCTYPE html>
<html>
<body>
<script>
var x = 35;
var y = 45;
var z = x + y;
document.write(z);
</script>
</body>
</html>
80
Local variables are declared inside a function and can only be accessed within that function.
function myFunction() {
var localVar = "I'm a local variable";
console.log(localVar); // This will work
}
console.log(localVar); // This will throw an error: localVar is not defined
Global variables are declared outside any function and can be accessed from any function in the script.
var globalVar = "global variable";
function myFunction() {
console.log(globalVar); // This will work
}
console.log(globalVar); // This will also work
Understanding how to correctly declare and use variables is fundamental in JavaScript programming, enabling you to store and manipulate data effectively.