2.0 KiB
id | title | challengeType | forumTopicId | dashedName |
---|---|---|---|---|
587d7da9367417b2b2512b67 | Add Elements to the End of an Array Using concat Instead of push | 1 | 301226 | add-elements-to-the-end-of-an-array-using-concat-instead-of-push |
--description--
Functional programming is all about creating and using non-mutating functions.
The last challenge introduced the concat
method as a way to combine arrays into a new one without mutating the original arrays. Compare concat
to the push
method. push
adds an item to the end of the same array it is called on, which mutates that array. Here's an example:
const arr = [1, 2, 3];
arr.push([4, 5, 6]);
arr
would have a modified value of [1, 2, 3, [4, 5, 6]]
, which is not the functional programming way.
concat
offers a way to add new items to the end of an array without any mutating side effects.
--instructions--
Change the nonMutatingPush
function so it uses concat
to add newItem
to the end of original
instead of push
. The function should return an array.
--hints--
Your code should use the concat
method.
assert(code.match(/\.concat/g));
Your code should not use the push
method.
assert(!code.match(/\.?[\s\S]*?push/g));
The first
array should not change.
assert(JSON.stringify(first) === JSON.stringify([1, 2, 3]));
The second
array should not change.
assert(JSON.stringify(second) === JSON.stringify([4, 5]));
nonMutatingPush([1, 2, 3], [4, 5])
should return [1, 2, 3, 4, 5]
.
assert(
JSON.stringify(nonMutatingPush([1, 2, 3], [4, 5])) ===
JSON.stringify([1, 2, 3, 4, 5])
);
--seed--
--seed-contents--
function nonMutatingPush(original, newItem) {
// Only change code below this line
return original.push(newItem);
// Only change code above this line
}
const first = [1, 2, 3];
const second = [4, 5];
nonMutatingPush(first, second);
--solutions--
function nonMutatingPush(original, newItem) {
return original.concat(newItem);
}
const first = [1, 2, 3];
const second = [4, 5];