freeCodeCamp/curriculum/challenges/english/02-javascript-algorithms-and-data-structures/functional-programming/remove-elements-from-an-array-using-slice-instead-of-splice.md

id, title, challengeType, forumTopicId, dashedName

id	title	challengeType	forumTopicId	dashedName
9d7123c8c441eeafaeb5bdef	Remove Elements from an Array Using slice Instead of splice	1	301236	remove-elements-from-an-array-using-slice-instead-of-splice

--description--

A common pattern while working with arrays is when you want to remove items and keep the rest of the array. JavaScript offers the splice method for this, which takes arguments for the index of where to start removing items, then the number of items to remove. If the second argument is not provided, the default is to remove items through the end. However, the splice method mutates the original array it is called on. Here's an example:

var cities = ["Chicago", "Delhi", "Islamabad", "London", "Berlin"];
cities.splice(3, 1);

Here splice returns the string London and deletes it from the cities array. cities will have the value ["Chicago", "Delhi", "Islamabad", "Berlin"].

As we saw in the last challenge, the slice method does not mutate the original array, but returns a new one which can be saved into a variable. Recall that the slice method takes two arguments for the indices to begin and end the slice (the end is non-inclusive), and returns those items in a new array. Using the slice method instead of splice helps to avoid any array-mutating side effects.

--instructions--

Rewrite the function nonMutatingSplice by using slice instead of splice. It should limit the provided cities array to a length of 3, and return a new array with only the first three items.

Do not mutate the original array provided to the function.

--hints--

Your code should use the slice method.

assert(code.match(/\.slice/g));

Your code should not use the splice method.

assert(!code.match(/\.?[\s\S]*?splice/g));

The inputCities array should not change.

assert(
  JSON.stringify(inputCities) ===
    JSON.stringify(['Chicago', 'Delhi', 'Islamabad', 'London', 'Berlin'])
);

nonMutatingSplice(["Chicago", "Delhi", "Islamabad", "London", "Berlin"]) should return ["Chicago", "Delhi", "Islamabad"].

assert(
  JSON.stringify(
    nonMutatingSplice(['Chicago', 'Delhi', 'Islamabad', 'London', 'Berlin'])
  ) === JSON.stringify(['Chicago', 'Delhi', 'Islamabad'])
);

--seed--

--seed-contents--

function nonMutatingSplice(cities) {
  // Only change code below this line
  return cities.splice(3);

  // Only change code above this line
}
var inputCities = ["Chicago", "Delhi", "Islamabad", "London", "Berlin"];
nonMutatingSplice(inputCities);

--solutions--

function nonMutatingSplice(cities) {
  // Only change code below this line
  return cities.slice(0,3);
  // Only change code above this line
}
var inputCities = ["Chicago", "Delhi", "Islamabad", "London", "Berlin"];
nonMutatingSplice(inputCities);