Replace array value from a specific position in JavaScript

To replace a value at a specific position in a JavaScript array, you can use the splice() method or direct index assignment. Both approaches modify the original array.

Using splice() Method

The splice() method removes elements and optionally adds new ones at a specified position.

Syntax

array.splice(index, deleteCount, newElement)

Example

var changePosition = 2;
var listOfNames = ['John', 'David', 'Mike', 'Sam', 'Carol'];

console.log("Before replacing:");
console.log(listOfNames);

var name = 'Adam';
var result = listOfNames.splice(changePosition, 1, name);

console.log("After replacing:");
console.log(listOfNames);
console.log("Removed element:", result);

Before replacing:
[ 'John', 'David', 'Mike', 'Sam', 'Carol' ]
After replacing:
[ 'John', 'David', 'Adam', 'Sam', 'Carol' ]
Removed element: [ 'Mike' ]

Using Direct Index Assignment

You can also replace array elements by directly assigning a new value to a specific index.

var fruits = ['apple', 'banana', 'orange', 'grape'];

console.log("Before replacement:");
console.log(fruits);

// Replace element at index 1
fruits[1] = 'mango';

console.log("After replacement:");
console.log(fruits);

Before replacement:
[ 'apple', 'banana', 'orange', 'grape' ]
After replacement:
[ 'apple', 'mango', 'orange', 'grape' ]

Comparison

Multiple Replacements with splice()

You can replace multiple consecutive elements using splice():

var numbers = [1, 2, 3, 4, 5, 6];

console.log("Original array:");
console.log(numbers);

// Replace 2 elements starting from index 2
numbers.splice(2, 2, 'A', 'B');

console.log("After replacing 2 elements:");
console.log(numbers);

Original array:
[ 1, 2, 3, 4, 5, 6 ]
After replacing 2 elements:
[ 1, 2, 'A', 'B', 5, 6 ]

Conclusion

Use splice() when you need to know what was removed or replace multiple elements. For simple single replacements, direct index assignment is faster and more straightforward.