In Javascript, variables are scoped with the
var keyword. When declaring variables with var, the variable is scoped to the current function. When assigning to a variable without using the var keyword, it is assumed you're talking about an already defined variable in the same or a higher scope. If none is found, the variable is created in the highest scope.
Bottom line: declare all your variables using
var.
JavaScript doesn't have block scope but it does have function-scope.
From : StackOverFlow
