vars-on-top

A var belongs to the whole function, no matter where it's written. Inside an if or a loop it looks local to that block, but it exists, as undefined, from the first line of the function. Writing every var at the top shows the scope the variable really has.

A var is at the top if only other variable declarations come before it. Directives such as "use strict" and import declarations may come first. A var in a block, or in a for loop's head, is always reported. let and const aren't checked.

Configure#

Off by default. To turn it on:

[lint.rules]
"vars-on-top" = "error" # or "warn"

Examples#

function total(items) {
  var sum = 0;
  for (var i = 0; i < items.length; i++) {
    var price = items[i].price;
    sum += price;
  }
  return sum;
}

function total(items) {
  var sum = 0;
  var i;
  var price;
  for (i = 0; i < items.length; i++) {
    price = items[i].price;
    sum += price;
  }
  return sum;
}

When not to use it#

If your code uses let and const, which are scoped to their block, turn on no-var instead.