Comparing problem with If else statement in Javascript

Question

I have two condition of my same JSON data:

{  
   "selectionId":124,
   "selectionDate":"2070-01-01",
   "selectionAudit":null,
   "letter":[  
      {  
         "letterNo":13,
         "letterId":1,
         "inout":"out",
         "inoutNo":"12332466544",
         "inoutDate":"2070-01-01",
         "letterIssuedSubBy":null,
         "letterFile":null,
         "representativeName":null,
         "representativeNameEng":null,
         "selectionId":124,
         "assessmentNo":null,
         "entryBy":"user98",
         "rStatus":"I",
         "others":null,
         "signatary":"qwerrt",
         "letterBox":null,
         "imageFile":null,
         "imageTitle":null,
         "reminderYesNo":"N"
      }
   ]
}

Same JSON with letter array empty structure :

  {  
       "selectionId":124,
       "selectionDate":"2070-01-01",
       "selectionAudit":null,
       "letter":[]
    }

All these values are stored in var trDataSecondTable; . I tried to compare if the letter is empty or not by using if condition:

  if(trDataSecondTable.letter != null) {
            console.log("asasfasdfdsfdsfds");
         $("#inoutDate").val(trDataSecondTable.letter[0].inoutDate);
         $("#inoutNo").val(trDataSecondTable.letter[0].inoutNo);
         $("#signatary").val(trDataSecondTable.letter[0].signatary);
     }
     else
     {
         console.log("entered in else part");
     }

Though "letter":[] is empty it is not entering into else part. While comparing i also tried trDataSecondTable.letter.length != 0 but also it is not entering into else part.

While comparing i also tried trDataSecondTable.letter.length != 0 but also it is not entering into else part That is the correct method to check for an empty array. There must be another issue in you logic. — Rory McCrossan
– Rory McCrossan, Commented Feb 6, 2019 at 10:07
if(typeof array != "undefined" && array != null && array.length != null && array.length > 0){} — Palak Jadav
– Palak Jadav, Commented Feb 6, 2019 at 10:11

jo_va · Accepted Answer · 2019-02-06 10:23:33Z

4

Your condition should check for both null and the length:

if (trDataSecondTable.letter != null && trDataSecondTable.letter.length > 0)

Is is important to check for null before accessing the length property as it guarantees you won't try to access the length property on null, which would raise an exception. This is important since data is rarely reliable.

Because of the && operator, if the first check fails, the second check won't be evaluated.

Actually, an even safer way would be to check if the value is truthy, as this will work for null and undefined:

if (trDataSecondTable.letter && trDataSecondTable.letter.length > 0)

edited Feb 6, 2019 at 10:23

answered Feb 6, 2019 at 10:08

jo_va

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1 Comment

Maheer Ali Over a year ago

can you tell why he should check for both?

Nina Scholz · Accepted Answer · 2019-02-06 10:08:24Z

1

You could check the length of the array.

if (trDataSecondTable.letter.length) {
    // letter has some elements
} else {
    // no elements
}

answered Feb 6, 2019 at 10:08

Nina Scholz

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Comments

Nicolae Maties · Accepted Answer · 2019-02-06 10:14:06Z

0

I think this condition is enough

if(trDataSecondTable.letter.length)

answered Feb 6, 2019 at 10:14

Nicolae Maties

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1 Comment

jo_va Over a year ago

It can be dangerous to dereference the length property without checking if letter is null or undefined first, even more with raw data.

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