=proto
duk_bool_t duk_is_undefined(duk_context *ctx, duk_idx_t index);

=stack
[ ... val! ... ]

=summary
<p>Returns 1 if value at <code>index</code> is either <code>undefined</code>, otherwise
returns 0.  If <code>index</code> is invalid, also returns 0.</p>

=example
if (duk_is_undefined(ctx, -3)) {
    /* ... */
}

=tags
stack

=introduced
1.0.0