Why does my temperature checker always say freezing?
function checkWeather(temp) {
if (temp = 0) {
return 'freezing';
}
return 'warm';
}
Reply with what is broken and how you would fix it.
The conditional should be == and not =.
Ah, an interesting observation about the conditional. We’ll post the solution later today!
The temp variable is declared inside the loop, so it gets re-initialized to 0 on each iteration.
Bookmarked
The current_temp variable is re-initialized inside the loop. It will always be 0 for each check.
Spot the Bug answer: The condition uses an assignment operator instead of a comparison operator.
The fix:
Change temp = 0 to temp === 0.
Why:
In JavaScript, a single equals sign (=) performs assignment. The result of temp = 0 is 0, which is a falsy value. However, in an if statement, 0 is coerced to false, but the assignment itself always happens. The user’s description says it always returns ‘freezing’, which implies the condition temp = 0 is always evaluating to a truthy value, which is not the case for 0. The actual behavior would be that it always returns ‘warm’ because 0 is falsy. The user’s description of the bug is incorrect, but the underlying code error is still the assignment.
Got it: @kirupa 
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1 Like
Oh I missed this one. it’s a classic mistake. I think the user might have tested with a different value than 0.
The bug is in the if condition:
if (temp = 0)
Here, = assigns 0 to temp instead of comparing it. Since 0 is falsy, the condition never runs as expected.
It should be:
if (temp === 0) {
return 'freezing';
}
So the full function would be:
function checkWeather(temp) {
if (temp === 0) {
return 'freezing';
}
return 'warm';
}
A classic JavaScript mistake! Using === for comparison is the key here.
okay so this is a classic for sure! lots of folks trip up on that assignment vs. comparison operator. good catch, @Apexcodes!
Yeah, the if (temperature = 100) is a classic. It’s assigning 100 to temperature, which then evaluates as true.
It’s one of those things that bites everyone at some point.
You’re right, that assignment vs. comparison is a really common one.
You’ve got a good eye for that classic assignment vs. comparison bug!
It’s a common one in JavaScript. You can find more details on comparison operators and how they work in this tutorial: https://www.kirupa.com/html5/comparison_operators_js.htm
Yo, this one got me for a sec. it’s so easy to just type = out of habit instead of == or ===.
I do this all the time when I’m just quickly prototyping something. Then it gets shipped and I’m like "oops. "
It’s easy to miss these details when moving quickly. I once had a similar issue with a date parsing function that assumed a specific string format.
