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# Chapter 2: What's your type?

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Introduction to Programming course, Chapter 2. Learn about the data types in JavaScript and how to use them.

http://i2p.sethmcl.com

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### Chapter 2: What's your type?

1. 1. chapter 2 what’s your type?
2. 2. expression semicolon ends the expression arithmetic operator value value 2 + 2;
3. 3. 2 + 2; value (number) value (number)
4. 4. Numbers Good for... Not good for... ● A person’s age ● Day of the month ● Time ● Score in a game ● A person’s name ● Day name (Friday, etc.) ● Mailing address ● Chat message
5. 5. Booleans A binary value, having two possible values called “true” and “false” Bool·e·an ˈbo͞olēən/
6. 6. Booleans var isAwake = true;
7. 7. Booleans var isAwake = true; keyword
8. 8. Booleans var isAwake = true; identifier
9. 9. Booleans var isAwake = true; boolean literal
10. 10. Booleans var isAwake = true; assignment operator
11. 11. Booleans var isAwake = true; keyword identifier assignment operator boolean literal
12. 12. Booleans var isAwake = true; var isSad = false;
13. 13. Booleans Boolean('Seth'); // evaluates to true Boolean(''); // evaluates to false Boolean(0); // evaluates to false Boolean(234); // evaluates to true
14. 14. Booleans Good for... ● Constructing logical expressions if (isAwake) { // do something }
15. 15. function add(number1, number2) { return number1 + number2; } Functions Group code into a reusable chunk.
16. 16. function add(number1, number2) { return number1 + number2; } Functions Group code into a reusable chunk. keyword
17. 17. Functions Group code into a reusable chunk. function add(number1, number2) { return number1 + number2; } function name
18. 18. Functions Group code into a reusable chunk. function add(number1, number2) { return number1 + number2; } argument argument
19. 19. Functions Group code into a reusable chunk. function add(number1, number2) { return number1 + number2; } function body
20. 20. Functions Group code into a reusable chunk. function add(number1, number2) { return number1 + number2; } keyword
21. 21. Functions Group code into a reusable chunk. function add(number1, number2) { return number1 + number2; } value to return
22. 22. Functions Group code into a reusable chunk. function add(number1, number2) { return number1 + number2; } keyword function name argument argument keyword value to return function body
23. 23. Functions function add(number1, number2) { return number1 + number2; } add(10, 55); // evaluates to 65 invoke the function
24. 24. Functions Good for... ● Organizing your code into reusable pieces ● Holding code to draw a character in a game ● Calculating some value
25. 25. Objects Store a group of values. var player = { score: 100, level: 3 };
26. 26. Objects Store a group of values. var player = { score: 100, level: 3 }; key value
27. 27. Objects // bracket notation player['score']; // evaluates to 100 // dot notation player.score; // evaluates to 100
28. 28. Objects var player = { score: 100, level: 3 }; player.isAlive = true; player.isAlive; // evaluates to true
29. 29. Objects var player = { score: 100, level: 3 }; player.score = player.score + 50; player.score; // evaluates to 150
30. 30. Objects player.totalScore = function () { return this.score * this.level; }; player.totalScore(); // evaluates to 450 (150 * 3)
31. 31. Built-in Objects Math.random(); // evaluates to a random number, // between 0 and 1 console.log('Hello World'); // prints string to // developer console
32. 32. Objects Good for... ● Storing player status in a game ● Grouping behavior with data
33. 33. Strings Store alphanumeric values: letters, words, sentences. Examples: Hello, my name is Bob. Seth t Seth23
34. 34. Strings var foo = "abc"; // correct var bar = 'abc'; // correct var biz = 'abc"; // incorrect Quoting styles.
35. 35. Strings 'Seth' + ' ' + 'McLaughlin'; // evaluates to // 'Seth McLaughlin' Adding strings (concatenation).
36. 36. Strings 'Seth' + 77; // evaluates to 'Seth77' Adding strings to numbers.
37. 37. Strings 'Seth' - 'McLaughlin'; // evaluates to NaN 'Seth' / 'McLaughlin'; // evaluates to NaN 'Seth' * 'McLaughlin'; // evaluates to NaN -, /, * operators do not apply to string values. NaN means “Not A Number” (invalid value)
38. 38. Strings 'Seth'.length; // evaluates to the number 4 'Seth'[1]; // evaluates to the string 'e' 'Seth'.indexOf('e'); // evaluates to the number 1 'Seth'.toUpperCase(); // evaluates to the string 'SETH' 'Seth'.toLowerCase(); // evaluates to the string 'seth' Some of the built-in properties.
39. 39. Strings Good for... ● Storing text ● A player’s name ● A website URL ● A chat message
40. 40. Arrays var friends = ['Richard', 'Tom', 'Susie']; Store a list of items. Richard Tom Susie
41. 41. Arrays push() -- add to end Richard Tom Susie
42. 42. Arrays push() -- add to end Richard Tom Susie friends.push('Sara');
43. 43. Arrays push() -- add to end Richard Tom Susie friends.push('Sara'); Sara
44. 44. Arrays unshift() -- add to beginning Richard Tom Susie
45. 45. Arrays unshift() -- add to beginning Richard Tom Susie friends.unshift('Sara');
46. 46. Arrays unshift() -- add to beginning Richard Tom Susie friends.unshift('Sara');
47. 47. Arrays unshift() -- add to beginning Richard Tom Susie friends.unshift('Sara'); Sara
48. 48. Arrays count the items Richard Tom Susie friends.length; // evaluates to 4 Sara
49. 49. Arrays Get an item Richard Tom Susie friends[2]; // evaluates to 'Tom' friends[0]; // evaluates to 'Sara' Sara
50. 50. null and undefined Special values to indicate a lack of value var foo; foo; // evaluates to undefined var bar = null; bar; // evaluates to null
51. 51. null and undefined function myFunction() { var age = 34 + 10; } myFunction(); // evaluates to undefined since the // function does not return a value
52. 52. null and undefined Boolean(undefined); // evaluates to false Boolean(null); // evaluates to false
53. 53. Review
54. 54. What does concatenation mean?
55. 55. What is the boolean value of 2 + '2';?
56. 56. Write a function to multiply two numbers together, and return the result.
57. 57. Create an array to hold a list of state names. How can you get the number of states in your list?
58. 58. Create an object to represent a person. This object should have two properties: ● name - a string ● sayHello - a function When the function sayHello is invoked, the person’s name should be printed to the browser’s console.
59. 59. Intro to Programming with Seth McLaughlin