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Finished Chapter 3.7 Global Object

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Jason Zhu 2021-01-09 18:39:39 +11:00
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notes/chap3_types_values_and_variables.md
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@ -516,6 +516,24 @@ Symbol.keyFor(t) // => "shared"
## 3.7 The Global Object ## 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 ## 3.8 Immutable Primitive Values and Mutable Object References
## 3.9 Type Conversions ## 3.9 Type Conversions