Sets

A set is a collection of values, such that no value appears more than once and the order in which the values occur in the set is irrelevant.

Operations are:

new Set(iter) — Creates and returns a new set containing the values in the iterable object iter (often an array). To create an empty set, omit iter. If iter is a map, the result is a set of [key, value] arrays.
set.has(value) — Tests if value is a member of set.
set.add(value) — Adds value to set if it is not already present, and returns set.
set.delete(value) — If value is in set, it is deleted. delete does not return set; it returns true if value was in set, and false otherwise.
set.clear() — Removes all values from set and returns undefined.
set.size — Returns the number of elements in set.

Maps

Maps are lookup tables. Each entry in a map consists of a key-value pair. Keys must be unique, but the same value may occur multiple times.

Operations are:

new Map() — Creates and returns a new, empty map.
new Map(array_or_set) — The array_or_set must consist of [key, value] arrays; this returns a map with those keys and values.
map.has(key) — Tests if map contains the given key.
map.set(key, value) — Sets or changes the value associated with key to value and returns the modified map.
map.get(key) — Returns the value associated with key, or undefined if key is not in the map.
map.delete(key) — Removes key and its associated value from
map. Returns true if map was changed, false if key wasn’t found in map.
map.clear() — Removes all values from map and returns undefined.
map.size — Returns the number of key-value pairs in map.

JavaScript has a Date object, which can be created in any of the following ways:

new Date() — Returns the current date and time in the browser’s time zone.
new Date(ms) — Returns the date that corresponds to the number of milliseconds since “epoch” (January 1, 1970).
new Date(year, month, day, hours, minutes, seconds, milliseconds) Up to five arguments may be omitted from the right end, for example, new Date(year, month, day). You cannot supply just a year, because a single argument will be taken as milliseconds. If the year is less than 100, 1900 will be added to it.
new Date(string) — Converts string into a Date, if possible, and returns it. The International Standard format is yyyy-mm-dd, but many other formats are recognized.

Operations are:

date.getFullYear() and date.setFullYear(year)
date.setFullYear may also be given month and day arguments.
date.getMonth() and date.setMonth(n), where n is 0 (January) to 11 (December).
date.getDate() and date.setDate(n), where n is 1 to 31.
date.getHours() and date.setHours(n), where n is 0 to 23.
date.getMinutes() and date.setMinutes(n), where n is 0 to 59.
date.getSeconds() and date.setSeconds(n), where n is 0 to 59.
date.getMilliseconds() and date.setMilliseconds(n), where n is 0 to 999.
date.getTime() and date.setTime(n), where n is milliseconds since epoch.
Date.now() also returns milliseconds since epoch but is shorter than new Date().getTime().
date.getDay() returns 0 to 6, where 0 means Sunday (regardless of where you are, and despite ISO 8601 specifying Monday as the first day of the week).