Check for duplicates in JavaScript Array of Objects

July 28, 2019

How to check whether an Array of Objects contain duplicates by key

Consider an Array of student Objects with each object having a key id. We have to perform a validation whether multiple objects with the same Id is present in the Array or not.

The above are Arrays of student Objects, one with duplicate id value and one without duplicate id value. To get the  Ids present in the Arrays we need to use the map() Method

 

Now we have two Arrays containing all the Id values of Objects.  The first one has unique Ids  and the second one has

duplicate Id 42342.

 

To check for duplicates in Arrays, we can create a set from the array. Sets will only have the unique items in the array

 

The second set only has 2 values as one of the values in the Array had a duplicate.

So, on comparing the length of the Array and size of the Set  we can determine id  Array has duplicates or not

 

 

The whole code to check whether an Array of objects contain key-value duplicates will look like this. We can use this

logic to validate requests to Node.JS APIs

 

 

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