Variables declared with var
have the special property that regardless of where they're declared in a function they "float" to the top
of the function and are available for use even before they're declared. That makes scoping confusing, especially for new coders. To keep confusion to
a minimum, var
declarations should happen before the variables they declare are used for the first time.
var x = 1; function fun(){ alert(x); // Noncompliant as x is declared later in the same scope if(something) { var x = 42; // Declaration in function scope (not block scope!) shadows global variable } } fun(); // Unexpectedly alerts "undefined" instead of "1"
var x = 1; function fun() { print(x); if (something) { x = 42; } } fun(); // Print "1"