Finished Chapter 3.7 Global Object

notes/chap3_types_values_and_variables.md

@@ -516,6 +516,24 @@ Symbol.keyFor(t) // => "shared"
 
 ## 3.7 The Global Object
 
+**Global Object**: properties of this JS object are globally defined identifiers, and are available to a JS program.
+* Usage: When JS interpreter starts (e.g. Node or new page in web browser), it creates a new global object and initialize its properties:
+  * Global constants: e.g. `undefined`, `Infinity`, and `NaN`
+  * Global functions: e.g. `isNaN()`, `parseInt()` (§3.9.2), and `eval()` (§4.12)
+  * Constructor functions: e.g. `Date()`, `RegExp()`, `String()`, `Object()`, and `Array()` (§3.9.2)
+  * Global objects: e.g. `Math` and `JSON` (§6.8)
+* Initialized properties can be viewed as reserved words (尽管不是).
+
+Global object in Node:
+* global object has property with name `global`.
+* In Node, we can refer the global object using the name `global` 
+
+Global obj in web browsers:
+* **Window object** act as a global obj for all JS code in the browser window.
+* Use `window` property of this global obj to refer it.
+
+Since ES2020, `globalThis` is used to refer to the global obj.
+
 ## 3.8 Immutable Primitive Values and Mutable Object References
 
 ## 3.9 Type Conversions