The scope of a variable is the region of your program in which it is defined. JavaScript variables have only two scopes.
Let’s see how the scope of variables works in JavaScript.
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.
<html> <body onload = checkscope();> <script> <!-- var myVar = "global"; // Declare a global variable function checkscope( ) { var myVar = "local"; // Declare a local variable document.write(myVar); } //--> </script> </body> </html>