typescript - JavaScript error: Cannot read property 'includes' of undefined - Stack Overflow

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I want to check if a data.objectId already exists in the array msgArr. For that I am running the code below:

var exists = msgArr.objectId.includes(data.objectId);

if(exists === false){
   msgArr.push({"objectId":data.objectId,"latLont":data.latLont,"isOnline":data.isOnline});
}

The array looks like the following:

var msgArr = [
  {isOnline:true,latLont:"123",objectId:"on0V04v0Y9"},
  {isOnline:true,latLont:"1",objectId:"FpWBmpo0RY"},
  {isOnline:true,latLont:"48343",objectId:"Qt6CRXQuqE"} 
 ]

I am getting the error below:

Cannot read property 'includes' of undefined

I want to check if a data.objectId already exists in the array msgArr. For that I am running the code below:

var exists = msgArr.objectId.includes(data.objectId);

if(exists === false){
   msgArr.push({"objectId":data.objectId,"latLont":data.latLont,"isOnline":data.isOnline});
}

The array looks like the following:

var msgArr = [
  {isOnline:true,latLont:"123",objectId:"on0V04v0Y9"},
  {isOnline:true,latLont:"1",objectId:"FpWBmpo0RY"},
  {isOnline:true,latLont:"48343",objectId:"Qt6CRXQuqE"} 
 ]

I am getting the error below:

Cannot read property 'includes' of undefined

• javascript
• typescript
• ecmascript-6

Share Improve this question Follow edited Aug 8, 2019 at 18:09 isherwood 61k1616 gold badges120120 silver badges168168 bronze badges asked Jan 6, 2017 at 18:02 Folky.HFolky.H 1,20444 gold badges1616 silver badges4040 bronze badges 6

• 5 msgArr is an array. It doesn't have an objectId. – Dave Newton Commented Jan 6, 2017 at 18:04
• @DaveNewton it has.. – Folky.H Commented Jan 6, 2017 at 18:04
• 1 @Folky.H: Then you have no problems. – user1106925 Commented Jan 6, 2017 at 18:05
• 1 Because msgArr is an array. It doesn't have an objectId. – user1106925 Commented Jan 6, 2017 at 18:06
• 1 If you're wondering how to search an array to see if contains an object with a particular ID, Google that and you'll find plenty of solutions. – user1106925 Commented Jan 6, 2017 at 18:08

 |  Show 1 more comment

3 Answers 3

Sorted by: Reset to default 19

As the comments say: the javascript array object has no property objectId.
Looking at the objects in this array it's clear that they have it, so to check if a certain element exists you can do so using Array.prototype.some method:

var exists = msgArr.some(o => o.objectId === data.objectId);

It's telling you that you're trying to access a property on an undefined object. The msgArr object doesn't have a property objectID at all, which means it's undefined. Since that doesn't exist, there's no way for it to have an includes property available of any type.

What you need is to access an object in the array, not the array itself. Something like msgArr[0].objectID would refer to an instantiated object. You could even use the array functions to check if something exists based on its objectID with a filter function.

First of all Dave Newton is right. An array doesn't have an objectId!

Maybe your "array" isn't a real array. Maybe it's an object which contains an array... I don't know... but in that case, you would have to code something like this:

var exist = msArr["objectId"] !== undefined

than "exist" which is a boolean contains the info if "msArr" has an property/field called "objectId"

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