数据类型

• MDN - JavaScript 数据类型和数据结构
• ECMAScript Data Types and Values

原始类型 (Primitive Values)

值一经定义无法修改

• Undefined
• Null
• Boolean
  • 取值仅限 true 和 false 。
• String
• Number / BigInt
• Symbol

Object

• key type: String or Symbol
• Object type: Number, String, Boolean, Symbol

new Number(3)

• Change prototype of object type will apply to primitive type

Symbol.prototype.hello = () => console.log("hello")
var a = Symbol("a");
a.hello(); // hello

Type Conversion

StringToNumber

• StringToNumber supports: DEC, BIN, OCT, HEX, scientific notation
• Normally using Number is better than parseInt and parseFloat

NumberToString

• Extreme large or small value will use scientific notation