Immutability

In Javascript whether a value passed by reference depends on it's type.

Strings and numbers are passed by value.

Objects (including arrays) are passed by reference.

Object.assign

{...obj, obj2}

[...arr, obj]

.filter()

.slice and .splice

.splice() — mutates the array directly, which makes it somewhat unhealthy to use in React, unless you go through the trouble of cloning the array beforehand.
.slice() — good, does not mutate the array directly, returns shallow clone of the array. Important to remember that if items are objects, they will not be cloned by .slice()

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Removing item from an array

// ES6+
items: [
    ...items.slice(0, i),
    ...items.slice(i + 1)
],


// by index
const items = ['a', 'b', 'c', 'd', 'e', 'f']
const i = 2
const filteredItems = items.slice(0, i).concat(items.slice(i + 1, items.length))
// ["a", "b", "d", "e", "f"]



// If you know the value
const items = ['a', 'b', 'c', 'd', 'e', 'f']
const valueToRemove = 'c'
const filteredItems = items.filter(item => item !== valueToRemove)
// ["a", "b", "d", "e", "f"]


// by index wit removeItem function
const items = ['a', 'b', 'c', 'd', 'e', 'f']
const removeItem = (items, i) => items.slice(0, i-1).concat(items.slice(i, items.length))
let filteredItems = removeItem(items, 3)
filteredItems = removeItem(filteredItems, 5)
//["a", "b", "c", "d"]

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