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

id, title, challengeType

id	title	challengeType
9d7123c8c441eeafaeb5bdef	Remove Elements from an Array Using slice Instead of splice	1

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); // Returns "London" and deletes it from the cities array
// cities is now ["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.

Tests

tests:
  - text: Your code should use the <code>slice</code> method.
    testString: assert(code.match(/\.slice/g), 'Your code should use the <code>slice</code> method.');
  - text: Your code should not use the <code>splice</code> method.
    testString: assert(!code.match(/\.splice/g), 'Your code should not use the <code>splice</code> method.');
  - text: The <code>inputCities</code> array should not change.
    testString: assert(JSON.stringify(inputCities) === JSON.stringify(["Chicago", "Delhi", "Islamabad", "London", "Berlin"]), 'The <code>inputCities</code> array should not change.');
  - text: <code>nonMutatingSplice(["Chicago", "Delhi", "Islamabad", "London", "Berlin"])</code> should return <code>["Chicago", "Delhi", "Islamabad"]</code>.
    testString: assert(JSON.stringify(nonMutatingSplice(["Chicago", "Delhi", "Islamabad", "London", "Berlin"])) === JSON.stringify(["Chicago", "Delhi", "Islamabad"]), '<code>nonMutatingSplice(["Chicago", "Delhi", "Islamabad", "London", "Berlin"])</code> should return <code>["Chicago", "Delhi", "Islamabad"]</code>.');

Challenge Seed

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

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

Solution

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