Question

This seems to be easy question, but I can’t find an answer for this..

For example if I have the following object:

  var a = {
    foo : "FOO",
    bar : "BAR"
  }

Now, if I want to list properties of the objec, I should do the following :

  for( var b in a ) {
    // do something
  }

or, I can do this :

  for( b in a ) {
    // do something
  }

But, which is the difference beetween these methods? Why to use “var” or why not to use “var” in for in loop?

Answer 1

If you use a variable that has not been declared before without prepending var, you create a global variable.

function scope() {
    a = "hi";      // global
    var b = "ho";  // local
}

---

However, there is no difference between

for (var b in a) { /* .. */ }

and

var b;
for (b in a) { /* .. */ }