What is wrong with this if statement logic in JavaScript?

Question

if(stringName.charAt(0) != 'Q' || stringName.charAt(0) != 'W' || stringName.charAt(0) != 'E'){

        SetID = "Yes";

    }

The above code when I use alert to popup the windows the value of My.String.charAt(0) is returning the correct value but I don't know why it goes inside the if statement and change the value of SetID to Yes

I'm trying to figure out what is wrong with it and really can't see anything

SetID is initialize to No

nipick: you really should store stringName.charAt(0) in a variable and use that instead of doing the look up multiple times. — epascarello
– epascarello, Commented Apr 6, 2012 at 13:50
This question is similar to: != operator not working in while loop condition when combined with || OR. If you believe it’s different, please edit the question, make it clear how it’s different and/or how the answers on that question are not helpful for your problem. — dumbass
– dumbass, Commented Jan 5 at 14:09

Pointy · Accepted Answer · 2012-04-06 13:47:14Z

9

You're using || but you probably mean && ...

The way it is now, it'll always be true. "If the character is not 'Q', or it's not 'W', or it's not 'E', then ..." — even if it is one of those characters, it will not be the others, so the expression evaluates to true.

answered Apr 6, 2012 at 13:47

Pointy

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1 Comment

Ali Over a year ago

OMG how stupid I'm really I should have thought of that logic once again.

Niet the Dark Absol · Accepted Answer · 2012-04-06 13:49:59Z

1

Let's break down your statement.

MyString.charAt(0) != 'Q'

Okay, so if it's not Q then it continues.

||

So if the character is Q, continue along the chain.

MyString.charAt(0) != 'W'

By this point we've established that either the character is NOT Q (in which case SetID = "Yes" is run), or it is IS Q. But if it is Q, then clearly it is not W, therefore this next condition is true and SetID = "Yes" is run.

You see? No matter what the character is, it passes the test.

I think you meant to use &&, not ||. If you use &&, then the SetID = "Yes" is only run if the character is NONE OF Q, W or E.

answered Apr 6, 2012 at 13:49

Niet the Dark Absol

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epascarello · Accepted Answer · 2012-04-06 13:53:42Z

1

Not an answer [too much code for a comment], but another possible solution using a reg exp

var stringName = "Quick";
if( (/^[QWE]/).test(stringName) ){
   SetID = "Yes";
}

answered Apr 6, 2012 at 13:53

epascarello

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