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branneman/1-array.js

Last active May 23, 2023 18:03
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1-array.js
// Array = ordered + indexed + duplicate values
// a.k.a. List
const arr = [1, 2, 3]
// size
arr.length //=> 3
// random-access
arr[1] // 2
// iteration
arr.map((x) => x + 10) //=> 11, 12, 13
arr.forEach()
for (const x of arr) {
x
}
// mutation
arr[1] = 20 // update any index
arr.unshift() // add at the start
arr.push() // add at the end
arr.shift() // remove from the start
arr.pop() // remove at the end
// conversion
const obj = { foo: 'Foo', bar: 'Bar' }
Object.values(obj) //=> ['Foo', 'Bar']
Object.entries(obj) //=> [ [ 'foo', 'Foo' ], ... ]
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2-object.js
// Object = not ordered + key-value pairs + duplicate values
// keys are strings
// a.k.a. Map, Dictionary, Associative array/collection,
// Lookup table, Hash (table/map)
const obj = { user: 'foo', email: 'foo@example.org' }
// size
Object.getOwnPropertyNames(obj).length //=> 2
// random-access
obj.user //=> 'foo'
obj['email'] //=> 'foo@example.org'
// iteration
Object.keys(obj) //=> ['user', 'email']
Object.values(obj) //=> ['foo', 'foo@example.org']
Object.entries(obj) //=> [['user', 'foo'], ...]
for (const [key, value] of Object.entries(obj)) {
key //=> 'user'
value //=> 'foo'
}
// mutation
obj.user = 'bar' // add/change the value of a property
delete obj.email // delete a key-value pair
// conversion
const arr = ['a', 'b']
Object.fromEntries(arr) //=> { '0': 'a', '1': 'b' }
// example
const sessions = {
'194dc20': { user: 'foo', email: 'foo@example.org' },
'5b631ed': { user: 'bar', email: 'bar@example.org' },
}
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3-1-set.js
// Set = ordered + unique values
const set = new Set([1, 2, 3])
// size
set.size //=> 3
// access
set.has(2) //=> true
// iteration
set.forEach((x) => {})
for (const x of set) {
x
}
// mutation
set.add(42) // adds 42
set.add(42) // no-op
set.delete(42)
set.clear()
// conversion
new Set([1, 2, 3])
Array.from(set) //=> [1, 2, 3]
new Set(Object.values({ foo: 'Foo' })) //=> Set { 'Foo' }
Raw
3-2-set-operations.js
// examples.js
const setA = new Set([1, 2, 3, 4])
const setB = new Set([2, 3])
const setC = new Set([3, 4, 5, 6])
isSuperset(setA, setB) // returns true
union(setA, setC) // returns Set { 1, 2, 3, 4, 5, 6 }
intersection(setA, setC) // returns Set { 3, 4 }
difference(setA, setB) // returns Set { 1, 4 }
// util/set-operations.js
// source: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Set#implementing_basic_set_operations
export function isSuperset(set, subset) {
for (const elem of subset) {
if (!set.has(elem)) {
return false
}
}
return true
}
export function union(setA, setB) {
const _union = new Set(setA)
for (const elem of setB) {
_union.add(elem)
}
return _union
}
export function intersection(setA, setB) {
const _intersection = new Set()
for (const elem of setB) {
if (setA.has(elem)) {
_intersection.add(elem)
}
}
return _intersection
}
export function difference(setA, setB) {
const _difference = new Set(setA)
for (const elem of setB) {
_difference.delete(elem)
}
return _difference
}
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4-1-map.js
// Map = ordered + key-value pairs
const map = new Map([
['foo', 'Foo'],
['bar', 'Bar'],
])
// size
map.size //=> 2
// access
map.has('foo') //=> true
map.get('bar') //=> 'Bar'
// iteration
map.keys() //=> ['foo', 'bar']
map.values() //=> ['Foo', 'Bar']
map.entries() //=> [['foo', 'Foo'], ['bar', 'Bar']]
map.forEach(([k, v]) => {})
for (const [key, value] of map) {
}
// mutation
map.set('baz', 'Baz')
map.delete('foo')
map.clear()
// conversion
new Map() // 2d array -> Map
Array.from(map) // Map -> 2d array
new Map(Object.entries(address)) // Object -> Map
Object.fromEntries(map) // Map -> Object
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4-2-map-usage.js
const users = new Map()
users.set('foo', { name: 'Foo', email: 'foo@example.org' })
users.set('bran', { name: 'Bran', email: 'bran@example.org' })
users.set('bar', { name: 'Bar', email: 'bar@example.org' })
// random-access:
users.get('bran')
// iterate in order:
for (const [username, user] of users) {
username
user
}
Raw
4-3-map-usage.js
const users = {
foo: { name: 'Foo', email: 'foo@example.org' },
bran: { name: 'Bran', email: 'bran@example.org' },
bar: { name: 'Bar', email: 'bar@example.org' },
}
const usersAdditional = new WeakMap()
usersAdditional.set(users.bran, { admin: true })
// access object with additional properties:
Object.assign({}, users.bran, usersAdditional.get(users.bran))
//=> { name: 'foo', email: 'bran@example.org', admin: true }
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5-1-stack.js
// Stack, natively with Array
const stack = []
stack.push(42) // add at the end
const val1 = stack.pop() // remove from the end
const val2 = stack[stack.length - 1] // peek at the end
Raw
5-2-stack-class.js
// Stack, implemented with Array
class Stack {
constructor(arr) {
this._stack = arr
}
push(val) {
this._stack.push(val)
}
pop() {
return this._stack.pop() // mutates arr
}
peek() {
return this._stack[this._stack.length - 1]
}
}
const stack = new Stack()
stack.push(42) // add at the end
stack.push(42) // add at the end
const val1 = stack.pop() // remove from the end
const val2 = stack.peek() // peek at the end
Raw
5-3-stack-unique.js
// Stack, implemented with Set
class UniqueStack {
constructor(arr) {
this._stack = new Set(arr)
}
push(val) {
this._stack.add(val)
}
pop() {
const arr = Array.from(this._stack)
const val = arr.pop() // mutates arr
this._stack = new Set(arr)
return val
}
peek() {
const arr = Array.from(this._stack)
const val = arr[arr.length - 1]
return val
}
}
const uniqueStack = new UniqueStack()
uniqueStack.push(42) // add at the end
uniqueStack.push(42) // no-op, duplicate
const val3 = uniqueStack.pop() // remove from the end
const val4 = uniqueStack.peek() // peek at the end
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6-queue.js
// Queue with Array (front to back)
const queue1 = []
queue1.push(42) // add at the end
const val1 = queue1.shift() // remove from the start
// Queue with Array (back to front)
const queue2 = []
queue2.unshift(42) // add at the start
const val2 = queue2.pop() // remove from the end
// Queue with Set is also possible
// [similar to UniqueStack impl.]
Raw
7-deque.js
// Deque with Array
const deque = []
deque.unshift(42) // add at the start
deque.push(42) // add at the end
const val1 = deque.shift() // remove from the start
const val2 = deque.pop() // remove at the end
// Deque with Set is also possible
// [similar to UniqueStack impl.]
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