CODEWITHSUNDEEP
javascriptif-statementundefinedtypeof
AKS
AKS

Reputation: 17326

NodeJS / JavaScript if statement not working

NodeJS (latest).

I have the following code. Why the first IF statement is not working as expected? The control doesn't go inside first IF statement.

I see valid console.log output for the first line in the following code and was expecting the first IF statement should execute its code too. But it doesn't; the 2nd IF statement works.

  console.log("-- inside create IP() qData['osType'] is set to :: " + qData['osType'])
  //--
  if ( qData['osType'] == 'undefined' ) {
    console.log("1 -- setting qData['osType'] = Linux by default for now. This should happen automatically.")
    qData['osType'] = 'Linux'
    console.log("1 -- inside create IP() if-statement-qData['osType'] and qData['osType'] is set to :: "+qData['osType'])
  }
  if ( typeof qData['osType'] == 'undefined' ) {
    console.log("2 -- setting qData['osType'] = Linux by default for now. This should happen automatically.")
    qData['osType'] = 'Linux'
    console.log("2 -- inside create IP() if-statement-qData['osType'] and qData['osType'] is set to :: "+qData['osType'])
  }
  qData['osType'] = 'Linux'
  //--

Upvotes: 0

Views: 916

Answers (3)

mscdex
mscdex

Reputation: 106698

If you're checking for undefined-ness you can do one of:

  • typeof foo === 'undefined'
  • foo === undefined
  • foo === void 0

Anything else is not actually (strictly) checking for an undefined value (including comparing a value directly with the string 'undefined').

Upvotes: 3

philraj
philraj

Reputation: 841

In your first if statement, qData['osType'] evaluates to undefined, but your comparison is checking whether undefined == "undefined". The string literal has a value and therefore isn't equal to undefined.

In your second if statement, typeof qData['osType'] evaluates to the string "undefined", so the expression evaluates to true and your code block is executed.

Upvotes: 2

Aikon Mogwai
Aikon Mogwai

Reputation: 5225

I think qData['osType'] == 'undefined' must be rewrite as qData['osType'] == undefined

My prefer to check

if(!qData.osType)

Upvotes: 1

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