Which JavaScript Array functions are mutating?

Question

I am writing an Array-derived class in JavaScript and need to know which functions to overload so that I can be aware of changes made to the array.

I know Array.push() and Array.splice() are mutating. Is there a definitive list of any others?

Answer 1

You can find the list on MDN as Mutator methods (along with Accessor and Iteration methods):

• copyWithin
• fill
• pop
• push
• reverse
• shift
• sort
• splice
• unshift

Answer 2

You can also use .concat(), before using your mutation method, to ensure you are not mutating your arrays, eg

const dontMutateMe = [4,5,1,2,3];
const sortArray = dontMutateMe.concat().sort(...)

Answer 3

I found this website called Doesitmutate

Have the list of all functions - and tells whether it mutates or not.