JavaScript error: Property 'includes' of undefined cannot be accessed

To verify the existence of data.objectId in the array msgArr, I am utilizing the following code snippet:


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

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

The current structure of the array is as shown below:


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

An error message that I encountered reads:

Cannot read property 'includes' of undefined

javascripttypescriptecmascript-6

Answer №1

According to the feedback provided, it appears that the javascript array object does not contain a property called objectId. However, upon closer inspection of the objects within this array, it is evident that they do have such a property. To verify the existence of a specific element, one can utilize the Array.prototype.some method:

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

Answer №2

This message is indicating that you are attempting to access a property on an undefined object. The object msgArr does not have a property named objectID, which means it is undefined. Since the property does not exist, there is no way for it to have an includes property of any type.

To resolve this issue, you should be accessing an object within the array, rather than the array itself. For example, using msgArr[0].objectID would reference an instantiated object. You can also utilize array functions to check if something exists based on its objectID using a filter function.

Answer №3

To begin with, it's important to note that Dave Newton is correct: an array does not possess an objectId.

It's possible that what you're referring to as an "array" isn't actually a true array. It could be an object that includes an array... I'm not entirely sure about the specifics, but if that's the case, you would need to implement something along these lines:

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

In this scenario, the variable "exist" will hold a boolean value indicating whether the "msArr" object has a property or field named "objectId."

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