Which JavaScript Array functions are mutating?

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

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(...)