The JavaScript warning "test for equality (==) mistyped as assignment (=)?" occurs when there was an assignment (
=
) when you would normally expect a test for equality (
==
).
Warning: SyntaxError: test for equality (==) mistyped as assignment (=)?
(Firefox only)
SyntaxError
warning which is reported only if
javascript.options.strict
preference is set to
true
.
There was an assignment (
=
) when you would normally expect a test for equality (
==
). To help debugging, JavaScript (with strict warnings enabled) warns about this pattern.
It is advisable to not use simple assignments in a conditional expression (such as
if...else
), because the assignment can be confused with equality when glancing over the code. For example, do not use the following code:
if (x = y) {
// do the right thing
}
If you need to use an assignment in a conditional expression, a common practice is to put additional parentheses around the assignment. For example:
if ((x = y)) {
// do the right thing
}
Otherwise, you probably meant to use a comparison operator (e.g.
==
or
===
):
if (x == y) {
// do the right thing
}