I can't get the alert to work properly

Question

set("mean",total/weight);
if (mean = "NaN") {
    alert("Error! Please use NUMBERS only");
}

i want the alert to only run when the result is NaN, the calculation works without the if statement so i know that is not the problem.

Use the comparison operator `==`, not `=` – Zach Saucier Mar 07 '14 at 01:54 — Zach Saucier, Mar 07 '14 at 01:54

score 3 · Answer 1 · answered Mar 07 '14 at 01:55

3

Use the isNaN function for the comparison:

if(isNaN(mean)){
    alert("Error! Please use NUMBERS only");
}

answered Mar 07 '14 at 01:55

Kevin Bowersox

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the calculation runs but now the alert pops up no matter what – user3373223 Mar 07 '14 at 02:06
nevermind, using a way to get around this. thanks though – user3373223 Mar 07 '14 at 02:25

score 1 · Answer 2 · edited May 23 '17 at 12:10

In JavaScript, mean = "NaN", with a single equals sets the value of mean. The if statement will then check the "trueness" of the value "NaN" which will evaluate to true. That is, your if(mean = "NaN") will first set mean to the literal string "NaN", and then test if("NaN").

Use a double equals (mean == "NaN") for equality comparison, and triple equals (mean === "NaN") for type and equality comparison.

However, mean == "NaN" will always return false because NaN is not the literal string "NaN" but a special value. Use isNaN(mean) instead.

score 0 · Answer 3 · answered Mar 07 '14 at 01:55

0

Change

if (mean = "NaN") {

to

if (mean == "NaN") {

in the first u set a value into a var, in the second u do a logical comparison

answered Mar 07 '14 at 01:55

Itay Moav -Malimovka

52,579
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score 0 · Answer 4 · answered Mar 07 '14 at 01:56

You are assgining a string "NaN" to mean, not comparison.

Also you can't use mean === NaN to check, because compare to NaN always return false.

To check whether is a NaN, you have to use isNaN function.

if (isNaN(mean)) {
    alert("Error! Please use NUMBERS only");
}

I can't get the alert to work properly

4 Answers4