How to remember if a method mutates the original array?

Question

I know I can find a list of mutator methods on MDN, still, in practice I always forget if methods like push() or reverse() mutates the original array or creates a new one. Is there a logic to why certain methods are mutators and some are non-mutators, so I can easily remember?

Answer 1

Maybe a helpful way to remember them is to identify the mutating methods and group them; there's only a small amount.

Add/remove from array:

• Array.prototype.fill() - overwrite elements anywhere
• Array.prototype.pop() - remove from right
• Array.prototype.push() - add to right
• Array.prototype.shift() - remove from left
• Array.prototype.unshift() - add to left
• Array.prototype.splice() - add/remove anywhere

Rearrange arrays:

• Array.prototype.sort() - rearrange elements using a sorting function
• Array.prototype.reverse() - reverse elements

Oddball:

• Array.prototype.copyWithin() - honestly, I've never used this method

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List of mutating array methods

• Array.prototype.copyWithin()
• Array.prototype.fill()
• Array.prototype.flat()
• Array.prototype.pop()
• Array.prototype.push()
• Array.prototype.reverse()
• Array.prototype.shift()
• Array.prototype.sort()
• Array.prototype.splice()
• Array.prototype.unshift()

List of non-mutating array methods

• Array.from() - create an array from an iterable
• Array.isArray() - check if a variable is an array
• Array.of() - create an array; function version of []
• Array.prototype.concat() - combine several arrays into a new single array
• Array.prototype.entries() - get iterator of key/value pairs
• Array.prototype.every() - check if every value matches a function
• Array.prototype.filter() - create an array of values matching a filter
• Array.prototype.find() - find a value using a function
• Array.prototype.findIndex() - find the index of a value using a function
• Array.prototype.flat() - flatten a nested array
• Array.prototype.flatMap() - create an new array using a mapping function
• Array.prototype.forEach() - run a side effect for each value
• Array.prototype.includes() - check if the array includes a value
• Array.prototype.indexOf() - find the index of a value by value
• Array.prototype.join() - combine values into a string using a separator
• Array.prototype.keys() - get iterator of keys
• Array.prototype.lastIndexOf() - find the index of a value by value, starting at the end
• Array.prototype.map() - create a new array using a mapping function
• Array.prototype.reduce() - fold over each value, producing a new value
• Array.prototype.reduceRight() - fold over each value, starting from the right, producing a new value
• Array.prototype.slice() - select a subarray
• Array.prototype.some() - check if some value matches a function
• Array.prototype.toLocaleString() - string representation of the array, uses toLocaleString on values
• Array.prototype.toString() - string representation of the array, uses toString on values
• Array.prototype.values() - get iterator of values
• Array.prototype[@@iterator]() - get default iterator