"var variable" returns undefined?

Question

When I run "var variable = true;" in chrome console I get "undefined" returned:

> var variable = true;
undefined

But when I run without "var" it returns true:

> variable = true;
true

Why is it returning "undefined" with "var"?

It's confusing cause I expected it would return true.

Answer 1

The first is a statement, while the second is an expression. While not quite the same, it is similar to C's rules:

// A statement that has no value.
int x = 5;

// An expression...
x = 10;

// ...that can be passed around.
printf("%d\n", x = 15);