Mutable and Immutable Arrays

Methods that change the original array (mutating methods):

push: Adds one or more elements to the end of an array and returns the new length of the array.
pop: Removes the last element from an array and returns that element.
shift: Removes the first element from an array and returns that element.
unshift: Adds one or more elements to the beginning of an array and returns the new length of the array.
splice: Changes the contents of an array by removing, replacing, or adding elements in place.
reverse: Reverses the order of elements in an array.
sort: Sorts the elements of an array in place.
fill: Fills all the elements of an array with a static value.
Methods that don't change the original array (non-mutating methods):

concat: Combines two or more arrays and returns a new array.
slice: Extracts a section of an array and returns a new array.
join: Joins all elements of an array into a string.
map: Creates a new array by applying a function to each element of the original array.
filter: Creates a new array with all elements that pass a test implemented by a provided function.
reduce: Applies a function against an accumulator and each element in the array (from left to right) to reduce it to a single value.
find: Returns the first element in the array that satisfies a provided testing function.
some: Checks if at least one element in the array satisfies a provided testing function.
every: Checks if all elements in the array satisfy a provided testing function.