Why is the loop variable declared without var?

Question

JavaScript

In the guides, the loop variable is always declared (except for the before declaration) with var
Here is an example:

for (var i in obj) {
    result += obj_name + "." + i + " = " + obj[i] + "<br>";
  }

In Flanagan's book, an example is this:

function extend(o, p) {
    for(prop in p) { 
    o[prop] = p[prop]; 
    }
    return o;
}

Question: why is prop specified without var? It becomes a property of the global object, right?

Answer 1

1) examples in books are synthetic (it works fine)
2) true

Answer 2

In general, var should be set only when the variable is first specified and only in strict mode, in other cases the interpreter will correct this error within itself