How to append a new key to an array of objects using JavaScript

Question

How to append a new key to an array of objects using JavaScript

I have encountered a small issue while trying to add the key 'greeting' to an array of objects. Although my code successfully adds the key, it also adds another array at the end when I log the result.

function greetDevelopers(list) {

list.greeting  = list.map(x => x.greeting = `Hi ${x.firstName}, what do 
you like most about ${x.language}?` );


console.log(list);


};

The output I am getting is as follows:

[ { firstName: 'Sofia',
    lastName: 'I.',
    country: 'Argentina',
    continent: 'Americas',
    age: 35,
    language: 'Java',
    greeting: 'Hi Sofia, what do you like most about Java?' },
  { firstName: 'Lukas',
    lastName: 'X.',
    country: 'Croatia',
    continent: 'Europe',
    age: 35,
    language: 'Python',
    greeting: 'Hi Lukas, what do you like most about Python?' },
  { firstName: 'Madison',
    lastName: 'U.',
    country: 'United States',
    continent: 'Americas',
    age: 32,
    language: 'Ruby',
    greeting: 'Hi Madison, what do you like most about Ruby?' },
  greeting: [ 'Hi Sofia, what do you like most about Java?',
    'Hi Lukas, what do you like most about Python?',
    'Hi Madison, what do you like most about Ruby?' ] ]

If anyone has any suggestions on how to ensure that each object retains the 'greeting' key without having it duplicated at the end, I would greatly appreciate it.

Many thanks.

javascript arrays object

Answer 1

Answer №1

Avoid assigning to list.greeting, as it will assign the result to the array itself, which is not recommended (arrays should only contain elements, not properties). Instead of creating a new array, focus on side-effects by using forEach instead of map. Here's an example where we log the modified array without assigning it to anything:

const input = [ { firstName: 'Sofia',
    lastName: 'I.',
    country: 'Argentina',
    continent: 'Americas',
    age: 35,
    language: 'Java',
  }, { firstName: 'Lukas',
    lastName: 'X.',
    country: 'Croatia',
    continent: 'Europe',
    age: 35,
    language: 'Python',},
  { firstName: 'Madison',
    lastName: 'U.',
    country: 'United States',
    continent: 'Americas',
    age: 32,
    language: 'Ruby',
}];

function greetDevelopers(list) {
  list.forEach((item) => {
    item.greeting = `Hi ${item.firstName}, what do you like most about ${item.language}?`;
  });
  console.log(list);
}
greetDevelopers(input);

Answer 2

Avoid assigning to list.greeting, as it will assign the result to the array itself, which is not recommended (arrays should only contain elements, not properties). Instead of creating a new array, focus on side-effects by using forEach instead of map. Here's an example where we log the modified array without assigning it to anything:

const input = [ { firstName: 'Sofia',
    lastName: 'I.',
    country: 'Argentina',
    continent: 'Americas',
    age: 35,
    language: 'Java',
  }, { firstName: 'Lukas',
    lastName: 'X.',
    country: 'Croatia',
    continent: 'Europe',
    age: 35,
    language: 'Python',},
  { firstName: 'Madison',
    lastName: 'U.',
    country: 'United States',
    continent: 'Americas',
    age: 32,
    language: 'Ruby',
}];

function greetDevelopers(list) {
  list.forEach((item) => {
    item.greeting = `Hi ${item.firstName}, what do you like most about ${item.language}?`;
  });
  console.log(list);
}
greetDevelopers(input);

Answer 3

Answer №2

To update each object in the array and create a new array, you will need to modify the list.greeting. Instead of just creating a new key, you should replace the existing greeting key in each object.

let inputArray = [{
  firstName: 'Sofia',
  lastName: 'I.',
  country: 'Argentina',
  continent: 'Americas',
  age: 35,
  language: 'Java'
}, {
  firstName: 'Lukas',
  lastName: 'X.',
  country: 'Croatia',
  continent: 'Europe',
  age: 35,
  language: 'Python'
}, {
  firstName: 'Madison',
  lastName: 'U.',
  country: 'United States',
  continent: 'Americas',
  age: 32,
  language: 'Ruby'
}]

function customizeGreetings(array) {

  let newArray = array.map(function(item) {
    item.greeting = `Hi ${item.firstName}, what do you like most about ${item.language}?`
    return item;
  })
 return newArray;
};
console.log(customizeGreetings(inputArray))

Answer 4

To update each object in the array and create a new array, you will need to modify the list.greeting. Instead of just creating a new key, you should replace the existing greeting key in each object.

let inputArray = [{
  firstName: 'Sofia',
  lastName: 'I.',
  country: 'Argentina',
  continent: 'Americas',
  age: 35,
  language: 'Java'
}, {
  firstName: 'Lukas',
  lastName: 'X.',
  country: 'Croatia',
  continent: 'Europe',
  age: 35,
  language: 'Python'
}, {
  firstName: 'Madison',
  lastName: 'U.',
  country: 'United States',
  continent: 'Americas',
  age: 32,
  language: 'Ruby'
}]

function customizeGreetings(array) {

  let newArray = array.map(function(item) {
    item.greeting = `Hi ${item.firstName}, what do you like most about ${item.language}?`
    return item;
  })
 return newArray;
};
console.log(customizeGreetings(inputArray))

How to append a new key to an array of objects using JavaScript

Answer №1

Answer №2

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