A global variable has global scope which means it can be defined anywhere in your JavaScript code.
Within the body of a function, a local variable takes precedence over a global variable with the same name. If you declare a local variable or function parameter with the same name as a global variable, you effectively hide the global variable.
Commonly, a global variable is declared like the following −
<html>
<body onload = checkscope();>
<script>
<!--
var myVar = "global"; // Declare a global variable
function checkscope() {
document.write(myVar);
}
//-->
</script>
</body>
</html>But, what you can above is the traditional method of using global variables. The best practice is to use it like the following with “window” −
<html>
<body onload = checkscope();>
<script>
window.myVar = "global"; // Declare a global variable
function checkscope( ) {
alert(myVar);
}
</script>
</body>
</html>