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Discussion on: Help with includes() in js

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vonheikemen profile image
Heiker • • Edited

Let's just say that Array.includes is making a "shallow comparison". What is happening is that you're comparing an object against a string. Imagine something like this.

'Oldest' === ({ id:3, name:'Oldest', another:'things' })
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If you try that it would return false.

Array.includes doesn't try to find the string inside the object it, just compares the whole item in the array against your argument.

If I were to try implement Array.includes as a function it would be like this.

function includes(array, search) {
   for(const item of array) {
      if(item === search) {
         return true;
      }
   }

   return false;
}
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magimart profile image
Magima Felix O •

i have to look into this approach, thank you very much for the response

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vonheikemen profile image
Heiker •

Actually I was just trying to explain how Array.includes works.

What would solve your problem is to transform formB into an array of names before using formA.filter. Like this.

const formBNames = formB.map((x) => x.name);

const difference = formA.filter((x) => !formBNames.includes(x.name));
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magimart profile image
Magima Felix O •

thank your very much for your kind efforts, i tried it like you stated already but got got a desirable result. i used a set method instead and worked well.
Another contribute here also commented with reducer() that also works perfect :)