JavaScript

JavaScript . , . . , :

var foo = 42; //  foo  Number
foo = "bar"; //   foo  String
foo = true; // foo   Boolean

ECMAScript 8 :

• 6 :

  • Undefined ( ) : typeof instance === "undefined"
  • Boolean (, ) : typeof instance === "boolean"
  • Number () : typeof instance === "number"
  • String () : typeof instance === "string"
  • BigInt : typeof instance === "bigint"
  • Symbol ( ECMAScript 6) : typeof instance === "symbol"

• Null (Null ) : typeof instance === "object". , ;

• Object () : typeof instance === "object". , , , new: new Object, new Array, new Map, new Set, new WeakMap, new WeakSet, new Date ;

typeof , .. "object" , typeof , . , instanceof, , .

typeof: "object" null "function" : , , , , - , "", .

JavaScript, , ( , ). , C, , JavaScript . .

: true () false (). Boolean Boolean .

Null

: null. null Null .

Undefined

, , undefined. undefined undefined .

ECMAScript, , 64- IEEE 754. , JavaScript . , () . , : +Infinity ( ), -Infinity ( ), NaN ( ).

+/-Infinity, Number.MAX_VALUE Number.MIN_VALUE. ECMAScript 2015, , , Number.isSafeInteger(), Number.MAX_SAFE_INTEGER Number.MIN_SAFE_INTEGER. , .

JavaScript : -0 +0. (0 +0). . , +0 === -0 . , :

> 42 / +0
Infinity
> 42 / -0
-Infinity

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C, JavaScript . , , , . . :

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(Symbol)

JavaScript ECMAScript 2015. , ( ). . (enum) C. Symbol Symbol.

(BigInt)

BigInt , , 2 53, , JavaScript Number .

> let bigInt = 19241924124n;
> console.log(bigInt);
19241924124n
> console.log(typeof bigInt);
"bigint"

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Date.

length. , Array.prototype, . , indexOf ( ), push ( ) . . .

, . " " , Int8Array, Float32Array .. . ArrayBuffer DataView.

: Maps, Sets, WeakMaps, WeakSets

, JavaScript ECMAScript Edition 6. Set WeakSet , Map WeakMap ( ) . Map WeakMap , Map . WeakMap.

Map Set ECMAScript 5. , , . ( WeakMap) .

, DOM, , data-*. , , . Maps WeakMaps .

: JSON

JSON (JavaScript Object Notation) , JavaScript, . JSON . JSON JSON .

JavaScript . , , .

typeof

typeof . , .

• Nicholas Zakas, , JavaScript.
• JavaScript