Replica an array and exchange one part at a selected index with fashionable JavaScript


How do you exchange an array part at a given index?

Is that this a trick query? No longer in point of fact.

const numbers = [1, 2, 3, 4, 5];
numbers[1] = 'new price';
console.log(numbers); 

However when you find yourself the use of React or any framework having a bet on immutability, simply converting an array access will result in refined insects since the array will nonetheless be the similar object with the similar reference. In an immutable global, knowledge updates all the time must lead to a brand new object reference.

How are you able to trade an array part by way of its index and spit out a brand new array in the similar move then? A 12-years-old Stack Overflow query with 1.5m perspectives has heaps of recommendation, however as a result of it is so outdated and has masses of upvotes, it isn’t appearing essentially the most fashionable answer within the most sensible house.

Let’s have a snappy take a look at ingenious solutions.

The outdated approach to reproduction an array and alter one merchandise

You unquestionably may just iterate over the array and increase a brand new one with a just right outdated forEach loop.

serve as changeItem(array, index, newValue) {
  const newArray = [];
  array.forEach((num, i) => {
    if (i === index ) go back newNumbers.push(newValue); 

    newArray.push(num);
  })
  go back newArray;
}

const numbers = [1, 2, 3, 4, 5];
const updatedNumbers = changeItem(numbers, 1, 'new price');
console.log(updatedNumbers);             
console.log(numbers === updatedNumbers); 

However this is not nice. Doing it with map is already somewhat nicer…

serve as changeItem(array, index, newValue) {
  go back array.map((price, i) => {
    if (i === index) go back newValue;

    go back price;
  })
}

const numbers = [1, 2, 3, 4, 5];
const updatedNumbers = changeItem(numbers, 1, 'new price');
console.log(updatedNumbers);              
console.log(numbers === updatedNumbers);  

And for the creatives, if you happen to belong to this small workforce of people who consider the adaptation between slice and splice, it is advisable to additionally use this kind of.

serve as changeItem(array, index, newValue) {
  go back [
    ...array.slice(0, index),
    newValue,
    ...array.slice(index + 1)
  ];
}

const numbers = [1, 2, 3, 4, 5];
const updatedNumbers = changeItem(numbers, 1, 'new price');
console.log(updatedNumbers);             
console.log(numbers === updatedNumbers); 

Ok, this one (☝️) is in truth horrible.

However what if I informed you that copying an array and converting one access is cross-browser supported in JavaScript these days?

The brand new method — reproduction an array and alter an access with with()

All fashionable browsers make stronger with() at the present time.

And with it, this whole workout turns into a nifty one-liner.

const numbers = [1, 2, 3, 4, 5];
const updatedNumbers = numbers.with(1, 'new price');
console.log(updatedNumbers);             
console.log(numbers === updatedNumbers); 

Thanks fashionable JavaScript!

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