JavaScript Array slice vs splice

In this post, we'll learn the difference between the JavaScript array methods slice() and splice() and when it's appropriate to use one over the other.

The difference between slice and splice is that slice is immutable whereas splice will mutate the array.

slice

The slice method will take an array and return a new array with the elements specified by the optional start and end parameters.

They're both optional so if you leave both blank, it will return the entire array.

	const array = [1, 2, 3, 4, 5];
const newArray = array.slice();

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

If you provide the start parameter, it will start at that index and go until the end of the array.

	const array = [1, 2, 3, 4, 5];
const newArray = array.slice(2);

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

The start parameter can be negative to start at the end of the array.

	const array = [1, 2, 3, 4, 5];
const newArray = array.slice(-2);

console.log(newArray); // [4, 5]

When you provide both the start and end parameters, it will return the elements between those two indexes.

	const array = [1, 2, 3, 4, 5];
const newArray = array.slice(1, 3);

console.log(newArray); // [2, 3]

splice

The splice method will directly modified the array, essentially adding or removing elements from it using the optional start and count parameters.

When you only provide the start parameter, it will remove all elements from that index to the end of the array.

	const array = [1, 2, 3, 4, 5];
array.splice(2);

console.log(array); // [1, 2]

When you provide both the start and count parameters, it will remove count number of elements, starting at the start index.

	const array = [1, 2, 3, 4, 5];
array.splice(1, 2);

console.log(array); // [1, 4, 5]

You can pass an unlimited number of parameters to the splice method. Every parameter after the count parameter will be added to the array.

	const array = [1, 2, 3, 4, 5];
array.splice(1, 2, "a", "b", "c");

console.log(array); // [1, "a", "b", "c", 4, 5]

This means that you can set count to 0 with additional parameters to add to the array.

	const array = [1, 2, 3, 4, 5];
array.splice(1, 0, "a", "b", "c");

console.log(array); // [1, "a", "b", "c", 2, 3, 4, 5]

Conclusion

Hopefully this post has helped you understand the difference between JavaScript array's slice and splice methods and how they work. Remember, the slice method is immutable and the splice method is mutable.

Resources

• Splice - MDN Web Docs
• Slice - MDN Web Docs

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