Checking if a variable is undefined returns the variable is undefined

Question

I have a statement in my code:

if(!(typeof options.duration[i] === 'undefined'))

I have written it correctly, seems that there is no mistake but the console is throwing error that:

TypeError: options.duration is undefined

It should not show this error.It does not make any sense.

p.s.w.g · Accepted Answer · 2014-03-13 16:27:36Z

3

The variable options.duration is undefined, so accessing item i from it will result in this error. Perhaps try:

if(typeof options.duration !== 'undefined')

Or if you need to check both options.duration and options.duration[i], try

if(typeof options.duration !== 'undefined' &&
   typeof options.duration[i] !== 'undefined')

answered Mar 13, 2014 at 16:27

p.s.w.g

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Thanks it worked. Plus, I think you should add () around both conditions.
– Muhammed Talha Akbar
Commented Mar 13, 2014 at 16:31
@MuhammedTalhaAkbar That's not necessary, but if you find it makes the code more readable, then yes, you can put the parentheses around each condition.
– p.s.w.g
Commented Mar 13, 2014 at 16:35

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Alnitak · Accepted Answer · 2014-03-13 16:27:17Z

1

For your test to succeed, the array options.duration must itself also be defined.

answered Mar 13, 2014 at 16:27

Alnitak

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And options as well
– Johan
Commented Mar 13, 2014 at 16:28
@Johan it is not necessary because it is surely defined. ;)
– Muhammed Talha Akbar
Commented Mar 13, 2014 at 16:32

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Guffa · Accepted Answer · 2014-03-13 16:31:03Z

1

You get that error because the duration property doesn't exist.

Check if the property exists before you try to check items in it:

if('duration' in options && typeof options.duration[i] !== 'undefined')

answered Mar 13, 2014 at 16:31

Guffa

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3 Answers 3