扩展知识点

JS

Primitive types：
- undefined : typeof instance === "undefined"
- Boolean : typeof instance === "boolean"
- Number : typeof instance === "number"
- String : typeof instance === "string"
- BigInt : typeof instance === "bigint"
- Symbol : typeof instance === "symbol"
- Object: typeof instance === "object"
  - Function: typeof instance === "function"
  - null : typeof instance === "object"
BigInt: arbitrary precision, 2n ** 53n === 9007199254740992n
String: immutable, use it as 'textual-data-only'
Symbol: unique identifier, Well-known Symbols(Symbol.hasInstance, Symbol.iterator)
Object: a collection of properties
- key is String or Symbol, value can be any type
- data property, accessor property
- hashmap ~= object
- Function, Array are also objects
Value Types and Reference Types，值类型和引用类型
Coercion: type convertion, too complex to avoid it! 3 * "3" = ?
== or ===, always use ===
- 1 == "1", true, perform type coercion
- 1 === "1", false
- Falsy Values: false, 0, "", null, undefined, NaN

CSS is NOT a programming language. CSS is what you use to selectively style HTML elements.
- p{color:red;}，This CSS selects paragraph text, setting the color to red
- 选择器（Selector），p
- 规则（Decalration/Rule），color: red;
  - 属性（Property），或属性名，color
  - 属性值（Property value），red
Cascade & Specificity & Inheritance，级联、优先级和继承，CSS最核心的概念
- 级联（Cascade）：一个元素可以被多个选择器命中
- 优先级（Specificity）：级联状态下，如何确定命中的规则
- 继承（Inheritance）：无特定规则，跟着感觉走，如color可继承、width不可继承