After watching Dan Abramov's egghead series on Redux, https://egghead.io/lessons/javascript-redux-the-single-immutable-state-tree, I quickly played around with how native array methods in javascript could be immutable. This is focused on the methods not like map, reduce, filter etc which already don't mutate the array.

immutable-array-methods.es6.js

const pop = (array) => array.splice(0, -1);

const push = (array, el) => [...array, el];

const splice = (array = [], startCount, deleteCount = 0, ...elements) => {
	const { length } = array;
	let remainder = startCount + deleteCount;

	if(startCount > length || startCount <= -length) {
		startCount = 0;
	} else if(startCount < 0) {
		startCount = length + startCount;
		const elementsRemain = length - startCount <= deleteCount;
		remainder = elementsRemain ? length : startCount + deleteCount; 
	}
	if(deleteCount < 0) deleteCount = 0;

	return [
		...array.slice(0, startCount),
		...elements,
		...array.slice(remainder)
	];
};

const shift = (array) => array.slice(1);

const reverse = (array) => {
	return [...array].reverse(); 
};		

export default const iam {
	pop,
	push,
	splice,
	shift,
	reverse
};

nice!