Normally, global variables are considered evil but in Javascript they are still used considerably.

var test = "test";
console.log(window.test == "test");

Okay, this one is usual and expected.

if (true)	{
var test = "new test";
}
console.log(window.test == "new test");

Declaring the same variable inside the expression also gives any variable global scope.

function smth()	{
var test = "no new test";
}
smth();
console.log(window.test != "no new test");

When the same variable is declared using ‘var’ keyword inside a function expression, it won’t have global impact.

function smth2()	{
test = "new new test";
}
smth2();
console.log(window.test == "new new test");

But when the same variable (test in our case) is used inside a function expression, it will continue it’s global effect.

function smth3()	{
test2 = "new variable";
}
smth3();
console.log(window.test2 == "new variable");

This case is a bit interesting and odd. Even though, test2 has not been declared earlier, it will be treated as global variable now.

Hope this help!