In certain contexts, such as if, while or for statements, expressions are automatically coerced into a boolean. Therefore, techniques such as double negation (!!foo) or casting (Boolean(foo)) are unnecessary and produce the same result as without the negation or casting.

Invalid:

if (!!foo) {}
if (Boolean(foo)) {}
while (!!foo) {}
for (; Boolean(foo);) {}

Valid:

if (foo) {}
while (foo) {}
for (; foo;) {}