Check if variable is undefined

Question

I've tried both these:

if foo
  if foo[0] == bar.baz[0]
    input.form-control-success(type="text")
  else
    input.form-control-danger(type="text")
else
  input(type="text")

unless foo === undefined
  if foo[0] == bar.baz[0]
    input.form-control-success(type="text")
  else
    input.form-control-danger(type="text")
else
  input(type="text")

But in both cases I get the error

Cannot read property '0' of undefined

on the line if foo[0] == bar.baz[0].

The situation is that sometimes foo is passed to pug, and sometimes it isn't.

foo is an array when it is passed, and if it is passed I need to do something based on whether it's x^th element is the same as another array's x^th element.

Try `if foo !== undefined` instead `if foo` – codtex Dec 12 '17 at 10:57 — codtex, Dec 12 '17 at 10:57

score 2 · Accepted Answer · edited Dec 12 '17 at 11:19

2

undefined is falsy in js...it looks like bar.baz may be your culprit.

edited Dec 12 '17 at 11:19

theonlygusti

11,032
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answered Dec 12 '17 at 11:08

adamz4008

660
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10

Your initial assumption was correct. You can't inspect these variables in chrome though because they're compiled server-side – theonlygusti Dec 12 '17 at 11:20

Crappy · Answer 2 · 2017-12-12T11:18:48.747

2

You can use typeof to check if a variable is undefined. It always returns a string.

if (typeof foo === 'undefined') {
  console.log('foo is undefined');
}

var foo = ['one', 'two', 'three'];

if (typeof foo !== 'undefined') {
  // access elements
  console.log(foo[0] + ', ' + foo[1] + ', ' + foo[2]);
}

edited Dec 12 '17 at 11:18

answered Dec 12 '17 at 11:11

Crappy

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Check if variable is undefined

2 Answers2