How can a function modify a value within an array without affecting the value outside of the same array?

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In order to modify a value within an array without affecting the value outside of the same array, you can create a new copy of the array and make the modifications there. This can be done in several ways:

1. Using the spread operator: Create a new array using the spread operator and modify the desired value within the new array. This will preserve the original array without modifying it.

const originalArray = [1, 2, 3, 4];

const newArray = [...originalArray];
newArray[2] = 5; // modifies the third value in the new array

console.log(originalArray); // [1, 2, 3, 4]
console.log(newArray); // [1, 2, 5, 4]

1. Using the Array.map() method: Create a new array by mapping over the original array and modifying the desired value within the new array. This will also preserve the original array without modifying it.

const originalArray = [1, 2, 3, 4];

const newArray = originalArray.map((value, index) => {
    if (index === 2) { // modifies the third value in the new array
        return 5;
    }
    return value;
});

console.log(originalArray); // [1, 2, 3, 4]
console.log(newArray); // [1, 2, 5, 4]

Both of these methods create a new array and modify the desired value within that new array, so the original array remains unchanged.