JS Comcepts : Date And Time,Maps,String,JSON

CREATION


new Date(year, month, date, hours, minutes, seconds, ms)

new Date(year, month, date)


let now = new Date();




ACCESSING DATE COMPONENTES

getFullYear()        getMonth()            getDate()                   getHours(), 

getMinutes(),        getSeconds(),    getMilliseconds()         getDay()

getUTCFullYear()   getUTCMonth(),    getUTCDay().        getTime()

getTimezoneOffset()

CALCULATING DATE DIFFERENCE

alert("The loop took ${end -start} ms"

/ we have date1 and date2, which function faster returns their difference in ms?
function diffSubtract(date1, date2) {
  return date2 - date1;
}

// or
function diffGetTime(date1, date2) {
  return date2.getTime() - date1.getTime();
}

PARSING DATE

let ms = Date.parse(''2013-02-21");

Keep updating ....

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MAPS :

Map is a collection of keyed data items, just like an Object. But the main difference is that Map allows keys of any type.

The main methods are:

• new Map() – creates the map.
• map.set(key, value) – stores the value by the key.
• map.get(key) – returns the value by the key, undefined if key doesn’t exist in map.
• map.has(key) – returns true if the key exists, false otherwise.
• map.delete(key) – removes the value by the key.
• map.clear() – clears the map
• map.size – returns the current element count.

ITERATION

• map.keys() – returns an iterable for keys,
• map.values() – returns an iterable for values,
• map.entries() – returns an iterable for entries [key, value], it’s used by default in for..of.

SET

Its main methods are:

• new Set(iterable) – creates the set, optionally from an array of values (any iterable will do).
• set.add(value) – adds a value, returns the set itself.
• set.delete(value) – removes the value, returns true if value existed at the moment of the call, otherwise false.
• set.has(value) – returns true if the value exists in the set, otherwise false.
• set.clear() – removes everything from the set.
• set.size – is the elements count.

// a number in JSON is just a number
alert( JSON.stringify(1) ) // 1

// a string in JSON is still a string, but double-quoted
alert( JSON.stringify('test') ) // "test"

alert( JSON.stringify(true) ); // true

alert( JSON.stringify([1, 2, 3]) ); // [1,2,3]

Namely:

• Function properties (methods).
• Symbolic properties.
• Properties that store undefined.

let user = {
  sayHi() { // ignored
    alert("Hello");
  },
  [Symbol("id")]: 123, // ignored
  something: undefined // ignored
};

alert( JSON.stringify(user) ); // {} (empty object)

let json = JSON.stringify(value[, replacer, space])

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