How to return an object from an array in JavaScript [duplicate]

Question

Create a function that takes an array of people objects and returns the first found astronaut object from the array.

This is the code that I have created;

function findFirstAstronaut(people) {
    for (let i = 0; i < people.length; i++) {
        if (people.astronaut[i] === false) {
            return null
        }
        else  if (people.astronaut[i]) {
            return people[i]
        }
    }

My code is run against this test;

describe("findFirstAstronaut", () => {
  it("returns null if no Astronaut is in the array", () => {
    expect(findFirstAstronaut([])).to.be.null;
  });

  it("returns a person object who is an astronaut", () => {
    const astronaut = { name: "Tim Peake", isAstronaut: true };
     expect(findFirstAstronaut([astronaut])).to.have.keys([
      "name",
      "isAstronaut"
    ]);
    expect(findFirstAstronaut([astronaut]).isAstronaut).to.be.true;
  });

  it("returns the first astronaut from the array", () => {
    const astronauts = [
      { name: "Johnny Karate", isAstronaut: false },
      { name: "Neil Armstrong", isAstronaut: true },
      { name: "Valentina Tereshkova", isAstronaut: true },
      { name: "Bert Macklin", isAstronaut: false },
      { name: "Eileen Collins", isAstronaut: true },
      { name: "Kip Hackman", isAstronaut: false }
    ];
    expect(findFirstAstronaut(astronauts)).to.eql({
      name: "Neil Armstrong",
      isAstronaut: true
    });
  });
});

How do I fix my code?

Is that a particular unit test framework?

Peter Mortensen
– Peter Mortensen

2018-12-24 23:36:31 +00:00
Commented Dec 24, 2018 at 23:36 — Peter Mortensen
– Peter Mortensen, Commented Dec 24, 2018 at 23:36

Toby · Accepted Answer · 2018-12-24 17:10:24Z

11

ES6 introduces a new way to achieve this, if ES6 is an option for you:

myArray.find(item => {
  return item.isAstronaut
})

Or even more abbreviated:

myArray.find(item => item.isAstronaut)

find() is a one of the new iterators, along with filter() and map() and others for more easily working with arrays. find() will return the first item in your array that matches the condition. The => or "arrow function" means that you do not need to explicitly include the return statement.

Comments

Nina Scholz · Accepted Answer · 2018-12-24 17:04:43Z

5

You need to use the index for the array.

people[i]                // for the object
people[i].isAstronaut    // for a property of the object

Then you need only a check if isAstronaut is true and return with the item.

At the end outside of the for loop, return null, for a not found astronaut.

If you check inside the loop, you will return too early with the wrong result.

function findFirstAstronaut(people) {
    for (let i = 0; i < people.length; i++) {
        if (people[i].isAstronaut) {
            return people[i];
        }
    }
    return null;
}

answered Dec 24, 2018 at 17:04

Nina Scholz

388k26 gold badges367 silver badges417 bronze badges

Comments

ellipsis · Accepted Answer · 2018-12-24 17:44:25Z

5

One liner

arr.filter(item => item.isAstronaut)[0]

answered Dec 24, 2018 at 17:44

ellipsis

12.2k2 gold badges19 silver badges33 bronze badges

4 Comments

Mario Ishac Over a year ago

Is this lazy or does it iterate through the entire array?

ellipsis Over a year ago

It iterates through the whole array and which ever elements passes the condition are pushed into new array and the new array is returned.

Mario Ishac Over a year ago

Thing is, if only the first element is needed, constructing that whole new array is slower than returning as soon as the first element is found.

ellipsis Over a year ago

You are right. Find should be uaed instead. But find is relatively new. Some browsers dont have support for that. If thats not an issue you can use find.

Tom O. · Accepted Answer · 2018-12-24 17:13:18Z

You could simply filter out array elements that have an isAstronaut property equal to false using Array.prototype.filter. I prefer filter to Array.prototype.find since ES6 isn't supported in every browser.

Once you have the filtered array simply take the element in the 0 index position. Something like below:

const astronauts = [{
    name: "Johnny Karate",
    isAstronaut: false
  },
  {
    name: "Neil Armstrong",
    isAstronaut: true
  },
  {
    name: "Valentina Tereshkova",
    isAstronaut: true
  },
  {
    name: "Bert Macklin",
    isAstronaut: false
  },
  {
    name: "Eileen Collins",
    isAstronaut: true
  },
  {
    name: "Kip Hackman",
    isAstronaut: false
  }
];

//Array destructuring to get the first astronaut:
var [firstAstronautFound] = astronauts.filter(el => el.isAstronaut);

//Line above is same as doing this:
//var firstAstronautFound = astronauts.filter(el => el.isAstronaut)[0];

console.log(firstAstronautFound.name);

Sonal Borkar · Accepted Answer · 2018-12-24 17:13:45Z

0

First, you may need to check whether there is any item in array or else return null.

Second, you have to check for the property

Third, you have to check for the value of the property isAstronaut

function findFirstAstronaut(people) {
   if (people.length > 0)
    {
      for (let i = 0; i < people.length; i++) {
         if (("name" in people[i]) && ("isAstronaut" in people[i])) {
           if (people[i].isAstronaut)
              return people[i];              
           else  
              return true;
       }
      }
     }
    else
      return null;
   }

answered Dec 24, 2018 at 17:13

Sonal Borkar

5591 gold badge6 silver badges12 bronze badges

Collectives™ on Stack Overflow

How to return an object from an array in JavaScript [duplicate]

5 Answers 5

Comments

Comments

4 Comments

Comments

Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

5 Answers 5

Comments

Comments

4 Comments

Comments

Comments

Linked

Related