本章主要参考来源：

W3C - JavaScript Tutorial

======================11.01=============================

• document.write()
  <script>document.write(5 + 6);</script>
  The document.write() method should only be used for testing. because if you use document.write() after an HTML document is fully loaded, it will delete all existing HTML.
• console.log()
  active the browser with F12.

======================11.03=============================

• Variables
  declare a JavaScript variable with the var keyword

======================11.04=============================

• Type Operator
  //Type operators are described in the JS Type Conversion chapter.

• typeof
  Returns the type of a variable
• instanceof
  Returns true if an object is an instance of an object type

• assignment | 赋值？
  =、+=、-=、*=、/=
• data type
  numbers, strings, arrays, objects and more（more？）
• function
  a block of code designed to perform a particular task.

======================11.05=============================

• object（被定义的对象）
• Scope | 作用域？
  ** the set of variables, objects, and functions you have access to**
  <pre>// code here can not use carName
  function myFunction() {var carName = "Volvo"; // code here can use carName}</pre>
• events
  <button onclick="this.innerHTML=Date()">The time is?</button>
• strings
• Numbers
  var x = 123;
  (100 + 23).valueOf(); // returns 123 from expression 100 + 23
  <br />
  x = "10 20"
  Number(x); // returns NaN

======================11.06=============================

• math

• math.
  document.getElementById("demo").innerHTML = Math.PI; // returns 3.141592653589793
• Math.round(x) returns the value of x rounded to its nearest integer:
• Math.pow(x,y) returns the value of x to the power of y:
• Math.sqrt(x) returns the square root of x:
• Math.abs(x) returns the absolute (positive) value of x:
• Math.ceil(x) returns the value of x rounded up to its nearest integer:
• Math.floor(x) returns the value of x rounded down to its nearest integer:
• Math.sin(x) returns the sine (a value between -1 and 1) of the angle x (given in radians).
• Math.min() and Math.max() can be used to find the lowest or highest value in a list of arguments:

• random
  Math.random(); // returns a random number
• date
  <pre>new Date() // current date and time
  new Date(milliseconds)
  new Date(dateString)
  new Date(year, month, day, hours, minutes, seconds, milliseconds)</pre>

======================11.07=============================

• array
  var cars = ["Saab", "Volvo", "BMW"];

  var fruits = ["Banana", "Orange", "Apple", "Mango"];
  document.getElementById("demo").innerHTML = fruits.toString();
  //The toString() method returns an array as a comma separated string.
  

• Booleans

• Comparisons
• Conditions

======================11.08=============================

• Switch （like c++）
  switch (new Date().getDay()) {
  case 6:
  text = "Today is Saturday";
  break;
  case 0:
  text = "Today is Sunday";
  break;
  default:
  text = "Looking forward to the Weekend";}
• loop

• for
• while

======================11.09=============================

• RegExp（正则表达式）
• errors
  try { Block of code to try}
  catch(err) { Block of code to handle errors}

======================11.10=============================

• Hoisting（变量声明提升）
  var x; // Declare x
  x = 5; // Assign 5 to x

  elem = document.getElementById("demo"); // Find an element
  elem.innerHTML = x;                     // Display x in the element
  

• Strict Mode
  "use strict";before the script statement
  ======================11.13=============================

• Automatic Type Conversions？
  document.getElementById("demo").innerHTML = "Hello" - "Dolly";// returns NaN

======================11.15=============================

• JSON——JavaScript Object Notation
  The JSON syntax is derived from JavaScript object notation syntax；
  JSON format is text only；
  Code for reading and generating JSON data can be written in any programming language.