freeCodeCamp/use-destructuring-assignment-with-the-rest-parameter-to-reassign-array-elements.english.md at 9ce8bbb4c09d4e3d135c85a1f53d481d0c909010

Randell Dawson 05f73ca409 fix(curriculum): Convert blockquote elements to triple backtick syntax for JavaScript Algorithms and Data Structures (#35992 )

* fix: convert js algorithms and data structures

* fix: revert some blocks back to blockquote

* fix: reverted comparison code block to blockquotes

* fix: change js to json

Co-Authored-By: Oliver Eyton-Williams <ojeytonwilliams@gmail.com>

* fix: convert various section to triple backticks

* fix: Make the formatting consistent for comparisons

2019-05-17 08:20:30 -05:00

2.4 KiB

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id, title, challengeType

id	title	challengeType
587d7b8a367417b2b2512b4c	Use Destructuring Assignment with the Rest Parameter to Reassign Array Elements	1

Description

In some situations involving array destructuring, we might want to collect the rest of the elements into a separate array. The result is similar to Array.prototype.slice(), as shown below:

const [a, b, ...arr] = [1, 2, 3, 4, 5, 7];
console.log(a, b); // 1, 2
console.log(arr); // [3, 4, 5, 7]

Variables a and b take the first and second values from the array. After that, because of rest parameter's presence, arr gets rest of the values in the form of an array. The rest element only works correctly as the last variable in the list. As in, you cannot use the rest parameter to catch a subarray that leaves out last element of the original array.

Instructions

Use destructuring assignment with the rest parameter to perform an effective Array.prototype.slice() so that arr is a sub-array of the original array source with the first two elements omitted.

Tests

tests:
  - text: <code>arr</code> should be <code>[3,4,5,6,7,8,9,10]</code>
    testString: assert(arr.every((v, i) => v === i + 3) && arr.length === 8);
  - text: <code>Array.slice()</code> should not be used.
    testString: getUserInput => assert(!getUserInput('index').match(/slice/g));
  - text: Destructuring on <code>list</code> should be used.
    testString: assert(code.replace(/\s/g, '').match(/\[(([_$a-z]\w*)?,){1,}\.\.\.arr\]=list/i));

Challenge Seed

const source = [1,2,3,4,5,6,7,8,9,10];
function removeFirstTwo(list) {
  "use strict";
  // change code below this line
  const arr = list; // change this
  // change code above this line
  return arr;
}
const arr = removeFirstTwo(source);
console.log(arr); // should be [3,4,5,6,7,8,9,10]
console.log(source); // should be [1,2,3,4,5,6,7,8,9,10];

Solution

const source = [1,2,3,4,5,6,7,8,9,10];
function removeFirstTwo(list) {
  "use strict";
  // change code below this line
  const [, , ...arr] = list;
  // change code above this line
  return arr;
}
const arr = removeFirstTwo(source);

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