javascript - JSHint considers a for-in variable 'bad'. What does this mean? - Stack Overflow

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The following code:

var things = {'foo':'bar'}
for ( thing in things ) {
  console.log(thing)
}

Consistently produces the following error in jshint:

Bad for in variable 'thing'.

I do not understand what makes the 'thing' variable 'bad' - as you can see, it is not being used anywhere else. What should I do differently to make jshint not consider this to be an error?

The following code:

var things = {'foo':'bar'}
for ( thing in things ) {
  console.log(thing)
}

Consistently produces the following error in jshint:

Bad for in variable 'thing'.

I do not understand what makes the 'thing' variable 'bad' - as you can see, it is not being used anywhere else. What should I do differently to make jshint not consider this to be an error?

• javascript
• syntax
• for-loop
• jshint

Share Improve this question Follow edited Apr 16, 2014 at 11:21 mikemaccana asked May 2, 2012 at 18:55 mikemaccanamikemaccana 123k110110 gold badges427427 silver badges529529 bronze badges 3

• 9 It's global, which is always bad (bad bad bad bad bad). Try for( var thing in things). Don't know if this is the reason for the error though :) – Felix Kling Commented May 2, 2012 at 18:57
• 1 JSHint wants for in variables to be defined in the local scope (i.e. not in an outer function). It's related to this issue: github.com/jshint/jshint/issues/329 – dave1010 Commented Nov 28, 2012 at 9:47
• 2 Since 'bad' is so vague, I submitted a pull request to jshint so that it explicitly states that the variable is global. – mikemaccana Commented Nov 28, 2012 at 12:04

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2 Answers 2

Sorted by: Reset to default 25

They always are - if they are not declared. Try adding var if thing has not been previously declared.

for ( var thing in things ) {
  console.log(thing)
}

or

var thing;

//more code

for ( thing in things ) {
  console.log(thing)
}

Here is your code slightly modified, make sure all is declared before usage.

var things = {'foo':'bar'}, thing;
for ( thing in things ) {
  console.log(thing)
}

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