Weird Instructions -> Add Elements to the End of an Array Using concat Instead of push

Affected page

https://www.freecodecamp.org/learn/javascript-algorithms-and-data-structures/functional-programming/add-elements-to-the-end-of-an-array-using-concat-instead-of-push

Your code

function nonMutatingPush(original, newItem) {
  // Only change code below this line
  return original.concat([newItem]); //[ 1, 2, 3, [ 4, 5 ] ]

  // Only change code above this line
}

const first = [1, 2, 3];
const second = [4, 5];
nonMutatingPush(first, second);

Expected behavior

Since newItem, which references an array should be added to the original array (per the instructions), I expected to pass the test. Instead it says “nonMutatingPush([1, 2, 3], [4, 5]) should return [1, 2, 3, 4, 5].”, which would be concatenating the two arrays, but it isn’t a non mutating alternative to .push() as the instructions suggest.

Screenshots

System

• Device: [laptop]
• OS: [macOS]
• Browser: [chrome]

Additional context

[jeremylt]

If we want users to learn a “non mutating push”, I think its better that the solution not provide an avenue to mutate the original arrays.

const first = [1, 2, 3];
const second = [4, 5];
const third = first.concat([second]);

third[3].push(6);
console.log(third); // [ 1, 2, 3, [ 4, 5, 6 ] ]
console.log(second); // [ 4, 5, 6 ] I hate this....

I think the current intended solution is fine but the wording describing it isn’t quite accurate.

[haplorhine]

@jeremylt The challenge doesn’t say anything about using a spread operator, instead it asks users to “Change the nonMutatingPush function so it uses concat to add newItem to the end of original instead of push”. Pushing an array to an array would produce an array in an array. Since “The concat() method is used to merge two or more arrays” (https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/concat) to replicate the effect of push one needs to put the array about to be “pushed” into a new array, so the outer array gets merged and the inner array stays intact. My suggestion would be, if replicating the push behaviour isn’t the case, but merging the two given arrays, the instructions should ask users to “Change the nonMutatingPush function so it uses concat to merge newItem with original, without altering const first and const second”