if statement in javascript always true

Question

So, I have the code, its not done, but all i want it to do is display one alert box if I write the word 'help', and say something else if anything else is entered.

function prompter() {
var reply = prompt("This script is made to help you learn about new bands, to view more info, type help, otherwise, just click OK") 
if (reply === 'help' || 'Help')
  {
  alert("This script helps you find new bands. It was originally written in Python 3.0.1, using Komodo IDE, but was then manually translated into Javascript. Please answer the questions honestly. If you have no opinion on a question, merely press OK without typing anything.")
  }
else
  {
  alert("Press OK to continue")
  }
};

but, what happens, is no matter what, the first alert box pops up, even if you press cancel! How should I fix this???

Andrew Whitaker · Accepted Answer · 2012-02-15 23:26:56Z

12

if (reply === 'help' || 'Help')

should be:

if (reply === 'help' || reply === 'Help')

since 'Help' is "truthy" and so the first part of the if will always be entered.

Of course, even better would be to do a case-insensitive comparison:

if (reply.toLowerCase() === 'help')

Example: http://jsfiddle.net/qvEPe/

answered Feb 15, 2012 at 23:26

Andrew Whitaker

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7 Comments

Timothy Jones Over a year ago

'Help' isn't truthy in this case, because there's no == - see my answer. However, 'Help' is true, because strings are 'true' unless there's an == operator around.

Andrew Whitaker Over a year ago

@TimothyJones: I'm not sure that's correct. As a non-boolean, 'Help' can't simply be true. It is coerced to true upon evaluation, however. In other words, type coercion occurs whether or not an == is present.

Timothy Jones Over a year ago

@AndrewWhitaker Yes, strings are coerced to true, unless they're empty. However, the 'truthyness' in Javascript only happens when there's an == present (truthyness is caused by the Abstract Equality Comparison Algorithm, which you can find in the ECMAScript Specification, 5th edition 11.9.3). So the string "0" is also coerced to true unless there's a == around. It's misleading to describe strings generally as truthy or not - since truthyness only happens in == comparisons.

nnnnnn Over a year ago

@TimothyJones - I disagree. "Truthyness" is a more general term than you seem to want to make it. Quick example: var x = 'A' || 'B'; - x will be 'A', not true, so it has not been coerced to true even though there's no == operator in sight. Surely that's an example of "truthyness"? (Unless you're trying to say it is coerced to true while simultaneously retaining its original string value, which is just getting silly.) Also, 0 == "0" doesn't coerce to true even though there's an ==...

Timothy Jones Over a year ago

@nnnnnn Javascript disagrees - if(0 == "0") console.log("true"); prints true :)

|

calebds · Accepted Answer · 2012-02-15 23:27:51Z

2

The problem is here:

if (reply === 'help' || 'Help') // <-- 'Help' evaluates to TRUE
                                //      so condition is always TRUE

The equality operator doesn't "distribute", try

if (reply === 'help' || reply === 'Help')

answered Feb 15, 2012 at 23:27

calebds

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Comments

JaredPar · Accepted Answer · 2012-02-15 23:27:38Z

1

The reason why it always pops up is that reply === 'help' || 'Help' evaluates as (reply === 'Help') || ('Help'). The string literal Help is always truthy in Javascript hence it always evaluates to truthy.

To fix this you need to compare reply to both values

if (reply === 'help' || reply === 'Help') {
  ...
}

Or if you want any case variant of help use a regex

if (reply.match(/^help$/i)) {
  ...
}

answered Feb 15, 2012 at 23:27

JaredPar

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Comments

Jeffrey Sweeney · Accepted Answer · 2012-02-15 23:28:55Z

1

Just change this: if (reply === 'help' || 'Help')

To this: if (reply === 'help' || reply === 'Help')

The or statement was not comparing the variable.

answered Feb 15, 2012 at 23:28

Jeffrey Sweeney

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Comments

Timothy Jones · Accepted Answer · 2012-02-16 00:12:11Z

0

The problem is this line:

 if (reply === 'help' || 'Help')

Because in JavaScript, objects and non-empty strings evaluate to true when used as a boolean. There are a couple of exceptions to this when using ==

 if("0") // true
 if("0" == true) // false

In general, it's not a good idea to use == or raw variables in if statements.

As others have pointed out, use

if (reply === 'help' || reply === 'Help')

Or better:

if (typeof reply === 'string' && reply.toLowerCase() === 'help')

instead.

edited Feb 16, 2012 at 0:12

answered Feb 15, 2012 at 23:29

Timothy Jones

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2 Comments

nnnnnn Over a year ago

Non-empty strings are truthy, not true - otherwise "string" === true would evaluate to true.

Timothy Jones Over a year ago

@nnnnnn You're right. I had thought that most uses of truthy in Javascript referred to "0" as well, but a quick google showed that's not the case. I'll update it.

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