.slice() Method ~ How to Remove an Item from an Array

[Aleksandar8]

Tell us what’s happening:
After 12 failed attempts to pass this challenge, I had to see solutions which lead me to some confusion:
The solution:

return state.slice(0, action.index).concat(state.slice(action.index + 1, state.length));

I do understand the first part of slice()-ing before concat(), but for the the second part of code (inside concat's parameter) I got 2 question:

1. What does the + 1 means in the beginIndex (first parameter) of the .slice method (*I know it adds +1 to the index number, but I mean what’s the logic behind it)?

2. Which .length of the state is the endIndex (second parameter) referring to - the current (original/non-modified) state or the modified shallow copy of the current state (to whom we are concatenating)?

   Your code so far

const immutableReducer = (state = [0,1,2,3,4,5], action) => {
switch(action.type) {
  case 'REMOVE_ITEM':
    // Don't mutate state here or the tests will fail
    return
  default:
    return state;
}
};

const removeItem = (index) => {
return {
  type: 'REMOVE_ITEM',
  index
}
}

const store = Redux.createStore(immutableReducer);

  **Your browser information:**

User Agent is: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/100.0.4896.127 Safari/537.36

Challenge: Remove an Item from an Array

Link to the challenge:

freeCodeCamp.org

[jenovs]

@Aleksandar8

What does the + 1 means in the beginIndex (first parameter) of the .slice method (*I know it adds +1 to the index number, but I mean what’s the logic behind it)?

slice goes from first argument up until, but no included the second argument.

Let’s say index is 2.
Then state.slice(0, index) will return [0, 1]
And state.slice(index, state.length) will return [2,3,4,5].
As you want to remove the element and index position, you can just start at the next position:
state.slice(index + 1, state.length) will return [3,4,5].
Also second argument for slice is optional. If it’s not there, then slice will go until the end of the array.

@Aleksandar8

Which .length of the state is the endIndex (second parameter) referring to - the current (original/non-modified) state or the modified shallow copy of the current state (to whom we are concatenating)?

Slice doesn’t mutate the original array. So length is always the same.