Probem with callback using callbacks for filters in Javascript

Question

First of all, please answer without giving me negative reputation, since I searched for this responsably before posting.

I want to filter an array of players, first the ones who has an "a" in their names, from these the ones who has an "e" and lastly from the ones who pass the two previously mentioned filters, the ones who start with z. I tried three methods individually no problems are all, but put together it does not filter, not even once.

const players2 = ["veron", "cambiasso", "batistuta", "zanetti", "Dalessandro", "zamerano", "cae", "cea", "cerini", "zii"];

const filter3 = (players) => (players.filter(
  player => {
    player.startsWith('z');
    return player;
  })

  .filter(
    player => {
      player.includes('e');

      return player;
    })

  .filter(
    player => {
      player.includes('a');

      return player;

    }
  ));


console.log("Argentineans players filtered are: " + filter3(players2));

dx_over_dt · Accepted Answer · 2020-07-19 20:32:33Z

1

filter()'s callback needs to return a boolean. Since you're always returning player, and that is always a truthy value, you're not filtering anything.

const players2 = ["veron", "cambiasso", "batistuta", "zanetti", "Dalessandro", "zamerano", "cae", "cea", "cerini", "zii"];

const filter3 = players => 
  players
    .filter(player => player.startsWith('z'))
    .filter(player => player.includes('e'))
    .filter(player => player.includes('a'));

console.log("Argentineans players filtered are: " + filter3(players2));

edited Jul 19, 2020 at 20:32

answered Jul 19, 2020 at 0:44

dx_over_dt

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Comments

user12407908 · Accepted Answer · 2020-07-19 00:49:12Z

0

.filter() expects a boolean from the callback to determine if the current item should be included in the result. Whatever it gets will be converted to boolean.

Also, you don't need to filter multiple times. Just do one with &&. Otherwise you're iterating multiple times, which is more computationally expensive than necessary.

const players2 = ["veron", "cambiasso", "batistuta", "zanetti", "Dalessandro", "zamerano", "cae", "cea", "cerini", "zii"];

const filter3 = (players) => players.filter(
  player => 
    player.startsWith('z') &&
    player.includes('e') &&
    player.includes('a')
);


console.log("Argentineans players filtered are: " + filter3(players2));

answered Jul 19, 2020 at 0:49

user12407908

Comments

charlietfl · Accepted Answer · 2020-07-19 00:49:46Z

0

It's not very efficient to chain numerous filter() when you can do it all in one. Each time you call it requires another iteration of the array returned from previous operation and another new array generated.

Use a && conditional to return a boolean.

const players2 = ["veron", "cambiasso", "batistuta", "zanetti", "Dalessandro", "zamerano", "cae", "cea", "cerini", "zii"];

const filter3 = (players) => players
  .filter(player => player.startsWith('z') && player.includes('e') &&player.includes('a') )
 

console.log("Argentineans players filtered are: " + filter3(players2));

answered Jul 19, 2020 at 0:49

charlietfl

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Comments

Unmitigated · Accepted Answer · 2020-07-19 00:50:14Z

0

The callback for filter should return a truthy value if the element should be kept and a falsey value otherwise. You should be returning the result of startsWith and includes instead of the player itself. Your code can be simplified to only one filter call as well:

const filter3 = (players) => players
  .filter(player => player.startsWith('z')&&player.includes('e')&&player.includes('a'));

const players2 = ["veron", "cambiasso", "batistuta", "zanetti", "Dalessandro", "zamerano", "cae", "cea", "cerini", "zii"];
const filter3 = (players) => players
  .filter(player => player.startsWith('z')&&player.includes('e')&&player.includes('a'));
console.log("Argentineans players filtered are: " + filter3(players2));

answered Jul 19, 2020 at 0:50

Unmitigated

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Comments

Andres Diaz · Accepted Answer · 2020-07-19 16:32:41Z

0

Thank you everybody for your replies.

I want to highlight the fact that I do know how to write a code to get the correct result, by writing each function individually and then call them with

console.log(function1(function2(function3(players2))));

The issue here for me is try and understand why arrow function callback is not working. After seeing your replies, this is getting much easier.

answered Jul 19, 2020 at 16:32

Andres Diaz

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2 Comments

dx_over_dt Over a year ago

If one of these answers your question, you should mark it as your answer.

dx_over_dt Over a year ago

I mean you should click the checkbox next to the answer. That makes it officially the answer to this question.

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