Restrict duplicate entries into array JavaScript

Question

I am trying to add Objects as elements into an array. I am able to restrict the first already added element but subsequent entries are being duplicated.

Here' the code:

onAddButtonPress(data, id, name){
  const items = this.props.items;

  if(items.length >= 1){
    items.forEach(i=>
      {
        if(i.id !== id){
          const arr = data.map(i=>{
            return i.name
          })
    this.props.addToShopList({id:id, arr:arr, name:name})
        }
      }
      )

  }
  else{
    const arr = data.map(i=>{
      return i.name
    })
  this.props.addToShopList({id:id, arr:arr, name:name})
  }     

}

How to stop this duplicate entries? Please suggest. Thanks!

What is your question? :)

Webber
– Webber

2019-03-27 09:38:48 +00:00
Commented Mar 27, 2019 at 9:38 — Webber
– Webber, Commented Mar 27, 2019 at 9:38
How to stop the duplicate entries @Webber

Saumay Paul
– Saumay Paul

2019-03-27 09:40:55 +00:00
Commented Mar 27, 2019 at 9:40 — Saumay Paul
– Saumay Paul, Commented Mar 27, 2019 at 9:40
@RobbyCornelissen yeah just saw that

Vladimir Bogomolov
– Vladimir Bogomolov

2019-03-27 09:41:43 +00:00
Commented Mar 27, 2019 at 9:41 — Vladimir Bogomolov
– Vladimir Bogomolov, Commented Mar 27, 2019 at 9:41

Robby Cornelissen · Accepted Answer · 2019-03-27 10:07:12Z

You're adding to the list from inside the loop, which doesn't seem right. There are also a number of unneeded checks and duplicated code.

This should be sufficient, using Array.prototype.some():

onAddButtonPress(data, id, name) {
  const items = this.props.items;

  if (!items.some(i => i.id === id)) {
    const arr = data.map(({name}) => name);
    this.props.addToShopList({id, arr, name});
  }
}

Complete class example:

class Test {
  constructor() {
    this.props = {
      items: [],
      addToShopList: (item) => this.props.items.push(item)
    };
  }
  
  onAddButtonPress(data, id, name) {
    const items = this.props.items;

    if (!items.some(i => i.id === id)) {
      const arr = data.map(({name}) => name);          
      this.props.addToShopList({id, arr, name});
    }
  }
}

const test = new Test();
test.onAddButtonPress([], 1, "One");
test.onAddButtonPress([], 2, "Two");
test.onAddButtonPress([], 2, "Two");

console.log(test.props.items);

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