Javascript foreach and for loop always loop once only when do array.push

Question

Javascript code loop once only when do array.push when put console.log(odgovor) it display everything good

getTacni() {
    this.storageService.getQuestions().then(items => {
      let odgovori: { id: number; answer: number }[] = [];
      let odgovor: { id: number; answer: number } = { id: null, answer: null };
      for (let i of items) {
        odgovor.id = i.id;
        odgovor.answer = i.tacan;
        console.log(odgovor);
      }
    });
  }

FAIL every element in odgovori is same

getTacni() {
    this.storageService.getQuestions().then(items => {
      let odgovori: { id: number; answer: number }[] = [];
      let odgovor: { id: number; answer: number } = { id: null, answer: null };
      for (let i of items) {
        odgovor.id = i.id;
        odgovor.answer = i.tacan;
        odgovori.push(odgovor);
      }
    });
  }

CertainPerformance · Accepted Answer · 2019-06-07 00:14:13Z

4

In both snippets, you've only created one object in memory, which you proceed to mutate many times - create each object inside the loop instead:

getTacni() {
  this.storageService.getQuestions().then(items => {
    const odgovori: { id: number; answer: number }[] = [];
    for (let i of items) {
      const odgovor: { id: number; answer: number } = { id: i.id, answer: i.tacan };
      odgovori.push(odgovor);
    }
  });
}

You also might consider using .map, which is a concise, functional, and readable way to transform every element of one array into another:

getTacni() {
  this.storageService.getQuestions().then(items => {
    const odgovor = items.map(({ id, tacan }) => ({ id, answer: tacan }));
  });
}

answered Jun 7, 2019 at 0:14

CertainPerformance

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Comments

Ghoul Ahmed · Accepted Answer · 2019-06-07 00:20:39Z

0

Try this:

getTacni() {
  this.storageService.getQuestions().then(items => {
    const odgovori: { id: number; answer: number }[] = [];
    for (let i of items) {
      odgovori.push({ id: i.id, answer: i.tacan });
    }
  });
}

answered Jun 7, 2019 at 0:20

Ghoul Ahmed

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