Finished Chapter 8.1.1 Function Declaration

notes/chap6_objects.md

@@ -462,14 +462,78 @@ What can/cannot be serialized?
 
 ## 6.9 Object Methods
 
+All JS objects (excpet explicitly created w/o prototype) inherits properties from `Object.prototype`. Hence they inherited some **primarily methods**, which are universally available.
+* `hasOwnProperty()`, `propertyIsEnumerable()`
+* `Object.create()`, `Object.keys()`
+* `toString`
+* ...
+
 ### 6.9.1 The toString() Method
 
+* `toString()` takes no arg, and returns a string that represents the value of obj.
+* Default `toString()` is not useful (e.g. shown below), each class define their own `toString()`
+
+```js
+let s = { x: 1, y: 1 }.toString();  // s evaluate to "[object Object]", without show real information
+```
+
+* We can redefine `toString()` method:
+
+```js
+let point = {
+    x: 1,
+    y: 2,
+    toString: function() { return `(${this.x}, ${this.y})`; }
+};
+
+String(point)    // => "(1, 2)": toString() is used for string conversions
+```
+
 ### 6.9.2 The toLocaleString() Method
 
+`toLocaleString()`:
+* All objs have this method
+* Purpose of this method: return a localized (vs. internationalization) string representation of the obj.
+* default `toLocaleString()` defined by Object call `toString()` directly
+* Date/Number class defin customized versions of `toLocaleString()` to format date, currency, time, etc.
+* User can create their own method:
+
+```js
+let point = {
+    x: 1000,
+    y: 2000,
+    toString: function() { return `(${this.x}, ${this.y})`; },
+    toLocaleString: function() {
+        return `(${this.x.toLocaleString()}, ${this.y.toLocaleString()})`;
+    }
+};
+point.toString()        // => "(1000, 2000)"
+point.toLocaleString()  // => "(1,000, 2,000)": note thousands separators
+```
+
 ### 6.9.3 The valueOf() Method
 
+`valueOf()`:
+* is called when JS needs to convert an obj to some non-string primitive type (e.g. number)
+* Many built-in class has its own `valueOf()`
+  * Date class define its `valueOf()` to convert dates to number, so can perform comparison
+
 ### 6.9.4 The toJSON() Method
 
+`toJSON()` method:
+* didn't get defined in `Object.prototype`;
+* `JSON.stringify()` looks for & invoke it on any object that will be serialized
+
+```js
+let point = {
+    x: 1,
+    y: 2,
+    toString: function() { return `(${this.x}, ${this.y})`; },
+    toJSON: function() { return this.toString(); }
+};
+JSON.stringify([point])   // => '["(1, 2)"]'
+```
+
 ## 6.10 Extended Object Literal Syntax
 
 ### 6.10.1 Shorthand Properties

notes/chap8_functions.md

@@ -0,0 +1,58 @@
+# Chapter 8. Functions
+
+**Function** = a block of JS code that's defined once but may be invoked multiple times.
+* *argument*: values provided by during invocation as function's parameters.
+* *return value*: computed by function using argument values
+* *invocation context*: value of `this` keyword for each invocation
+
+Utilization of functions:
+* **method of object**: if function is assigned to a property of an obj.
+* When a function is invoked on an object (e.g. `obj.method()`), this object become invocation context (aka `this`) for the function
+* **Constructor**: function designed to initialize a new obj.
+
+Function as **first class citizen** (object):
+* In JS, functions are obj. Hence, can be manipulated by programs
+* We can set properties on functions and invoke methods on them (i.e. pass function as parameter to method)
+
+JS function definitions can be nested within other functions
+
+## 8.1 Defining Functions
+
+### 8.1.1 Function Declarations
+
+**Function declaration** = `function` keyword + Identifier as function name + `(param1, param2, ...)` + `{JS statements as function body}`
+* `return` causes function to stop executing and return computed value to caller
+* if body has no `return`, value of function is `undefined`
+
+```js
+// Print the name and value of each property of o.  Return undefined.
+function printprops(o) {
+    for(let p in o) {
+        console.log(`${p}: ${o[p]}\n`);
+    }
+}
+
+// Compute the distance between Cartesian points (x1,y1) and (x2,y2).
+function distance(x1, y1, x2, y2) {
+    let dx = x2 - x1;
+    let dy = y2 - y1;
+    return Math.sqrt(dx*dx + dy*dy);
+}
+
+// A recursive function (one that calls itself) that computes factorials
+// Recall that x! is the product of x and all positive integers less than it.
+function factorial(x) {
+    if (x <= 1) return 1;
+    return x * factorial(x-1);
+}
+```
+
+* Name of function (in function declaration) becomes a variable, whose value is function itself.
+* function declaration statements are "hoisted" (level up) to top of enclosing block.
+  * All function in a JS block will be defined before JS interpreter start execution
+
+### 8.1.2 Function Expressions
+
+Function Expression (FE 函数表达式) vs Function Declaration (FD 函数声明):
+* FE appear within context of a larger expression
+*