Error while sorting array of objects Cannot assign to read only property '2' of object '[object Array]'

Question

I'm having array of objects where object looks like this (values change):

   {
     stats: {
        hp: 2,
        mp: 0,
        defence: 4,
        agility: 11,
        speed: 6,
        strength: 31
     }
   }

I want to sort them in descending order by speed doing:

  array.sort((a, b) => {
            return b.stats.speed - a.stats.speed
        })

However I'm getting this error and I can't really decipher whats going on:

TypeError: Cannot assign to read only property '2' of object '[object Array]'

What am I missing?

Edit: Array of object in redux store:

const enemyDefaultState = [
{
    name: 'European Boy1',
    stats: {
        hp: 2,
        mp: 0,
        defence: 4,
        agility: 11,
        speed: 6,
        strength: 31
    }
},
{
    name: 'European Boy2',
    stats: {
        hp: 2,
        mp: 0,
        defence: 4,
        agility: 4,
        speed: 2,
        strength: 31
    }
},
{
    name: 'European Boy3',
    stats: {
        hp: 2,
        mp: 0,
        defence: 4,
        agility: 7,
        speed: 7,
        strength: 31
    }
},

]

I import the array and assign it to the variable:

 let enemies = getState().enemy;
        if (enemies) {
            //sort by speed stat
            enemies.sort((a, b) => {
                return b.stats.speed - a.stats.speed
            })
        }

Answer 1

Because the array is frozen in strict mode, you'll need to copy the array before sorting it:

array = array.slice().sort((a, b) => b.stats.speed - a.stats.speed)

Answer 2

The reason as Patrick stated is because the array is frozen. So any method of copying the array will work such as the one he suggests.

array = array.slice().sort((a, b) => b.stats.speed - a.stats.speed)

I just want to add that the reason the array is frozen in your case is because your using the array as props from the redux store and props in React are immutable hence your not being able to mutate the array.

Answer 3

The array is frozen to prevent mutation of the redux state. You use react cloneElement(): https://reactjs.org/docs/react-api.html#cloneelement

[...enemies].sort((a, b) => {
                return b.stats.speed - a.stats.speed
            })