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Chapter 2: What's your type?

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Seth McLaughlin
Seth McLaughlin

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?
expression semicolon ends the expression arithmetic operator value value 2 + 2;
2 + 2; value (number) value (number)
Numbers Good for... Not good for... ¡ñ A person¡¯s age ¡ñ Day of the month ¡ñ Time ¡ñ Score in a game ¡ñ A person¡¯s name ¡ñ Day name (Friday, etc.) ¡ñ Mailing address ¡ñ Chat message
Booleans A binary value, having two possible values called ¡°true¡± and ¡°false¡± Bool¡¤e¡¤an ?bo?ol¨¥?n/
Booleans var isAwake = true;
Booleans var isAwake = true; keyword
Booleans var isAwake = true; identifier
Booleans var isAwake = true; boolean literal
Booleans var isAwake = true; assignment operator
Booleans var isAwake = true; keyword identifier assignment operator boolean literal
Booleans var isAwake = true; var isSad = false;
Booleans Boolean('Seth'); // evaluates to true Boolean(''); // evaluates to false Boolean(0); // evaluates to false Boolean(234); // evaluates to true
Booleans Good for... ¡ñ Constructing logical expressions if (isAwake) { // do something }
function add(number1, number2) { return number1 + number2; } Functions Group code into a reusable chunk.
function add(number1, number2) { return number1 + number2; } Functions Group code into a reusable chunk. keyword
Functions Group code into a reusable chunk. function add(number1, number2) { return number1 + number2; } function name
Functions Group code into a reusable chunk. function add(number1, number2) { return number1 + number2; } argument argument
Functions Group code into a reusable chunk. function add(number1, number2) { return number1 + number2; } function body
Functions Group code into a reusable chunk. function add(number1, number2) { return number1 + number2; } keyword
Functions Group code into a reusable chunk. function add(number1, number2) { return number1 + number2; } value to return
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
Functions function add(number1, number2) { return number1 + number2; } add(10, 55); // evaluates to 65 invoke the function
Functions Good for... ¡ñ Organizing your code into reusable pieces ¡ñ Holding code to draw a character in a game ¡ñ Calculating some value
Objects Store a group of values. var player = { score: 100, level: 3 };
Objects Store a group of values. var player = { score: 100, level: 3 }; key value
Objects // bracket notation player['score']; // evaluates to 100 // dot notation player.score; // evaluates to 100
Objects var player = { score: 100, level: 3 }; player.isAlive = true; player.isAlive; // evaluates to true
Objects var player = { score: 100, level: 3 }; player.score = player.score + 50; player.score; // evaluates to 150
Objects player.totalScore = function () { return this.score * this.level; }; player.totalScore(); // evaluates to 450 (150 * 3)
Built-in Objects Math.random(); // evaluates to a random number, // between 0 and 1 console.log('Hello World'); // prints string to // developer console
Objects Good for... ¡ñ Storing player status in a game ¡ñ Grouping behavior with data
Strings Store alphanumeric values: letters, words, sentences. Examples: Hello, my name is Bob. Seth t Seth23
Strings var foo = "abc"; // correct var bar = 'abc'; // correct var biz = 'abc"; // incorrect Quoting styles.
Strings 'Seth' + ' ' + 'McLaughlin'; // evaluates to // 'Seth McLaughlin' Adding strings (concatenation).
Strings 'Seth' + 77; // evaluates to 'Seth77' Adding strings to numbers.
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)
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.
Strings Good for... ¡ñ Storing text ¡ñ A player¡¯s name ¡ñ A website URL ¡ñ A chat message
Arrays var friends = ['Richard', 'Tom', 'Susie']; Store a list of items. Richard Tom Susie
Arrays push() -- add to end Richard Tom Susie
Arrays push() -- add to end Richard Tom Susie friends.push('Sara');
Arrays push() -- add to end Richard Tom Susie friends.push('Sara'); Sara
Arrays unshift() -- add to beginning Richard Tom Susie
Arrays unshift() -- add to beginning Richard Tom Susie friends.unshift('Sara');
Arrays unshift() -- add to beginning Richard Tom Susie friends.unshift('Sara');
Arrays unshift() -- add to beginning Richard Tom Susie friends.unshift('Sara'); Sara
Arrays count the items Richard Tom Susie friends.length; // evaluates to 4 Sara
Arrays Get an item Richard Tom Susie friends[2]; // evaluates to 'Tom' friends[0]; // evaluates to 'Sara' Sara
null and undefined Special values to indicate a lack of value var foo; foo; // evaluates to undefined var bar = null; bar; // evaluates to null
null and undefined function myFunction() { var age = 34 + 10; } myFunction(); // evaluates to undefined since the // function does not return a value
null and undefined Boolean(undefined); // evaluates to false Boolean(null); // evaluates to false
Review
What does concatenation mean?
What is the boolean value of 2 + '2';?
Write a function to multiply two numbers together, and return the result.
Create an array to hold a list of state names. How can you get the number of states in your list?
Create an object to represent a person. This object should have two properties: ¡ñ name - a string ¡ñ sayHello - a function When the function sayHello is invoked, the person¡¯s name should be printed to the browser¡¯s console.
Intro to Programming with Seth McLaughlin

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Chapter 2: What's your type?