Readme.md

Types

---

Types

Variables

Loosely typing

A variable is a named placeholder for a value of any type.

definition

var variable_name;

initialization

var variable_name = "value";

var variable_name = "value";  // variable_name is a string
variable_name = 123;          // variable_name is now a number

var uninitializated; // variable not initializated
uninitializated;     // holds the special value `undefined`

---

Types

Data types

There are five simple data types (or primitive types):

• undefined
• null
• boolean
• number
• string

and one complex data type:

• object

---

Types

Undefined

undefined is a special value a variable holds if it isn't initialized

undefined is not a reserved word

var undefined = "hello"; // legal but not reccomended

---

Types

Null

null is a special value used to represent a null value

null is a reserved word

var null = "hello"; // SyntaxError: Unexpected token null

---

Types

Booleans

Boolean data type has only two values:
true and false, used without quotes.

var t = true;
var f = false;

---

Types

Numbers

var int = 1;
var float = 3.14;

var float1 = .07;  //missing decimal - interpreted as 0.07 preferred
var float2 = 1.;   //missing digit after decimal - interpreted as integer 1
var float3 = 10.0; //whole number - interpreted as integer 10

var octal1 = 070;  //octal for 56
var octal2 = 079;  //invalid octal - interpreted as 79
var octal3 = 008;  //invalid octal - interpreted as 8

var hex1 = 0x0;    //hexadecimal for 0
var hex2 = 0xA;    //hexadecimal for 10
var hex3 = 0X1F;   //hexedecimal for 31

var exp1 = 1e+1;   //1 * 10^1 = 10
var exp2 = 2e+3;   //2 * 10^3 = 2000
var exp3 = 123e-3; //123 * 10^-3 = 0.123

---

Types

Numbers

Range of Values

Number.MIN_VALUE;          // 5e-324 is the smallest representable number    
Number.MAX_VALUE;          // 1.7976931348623157e+308 is the largest representable number
Number.POSITIVE_INFINITY;  // the positive inifinity
Number.NEGATIVE_INFINITY;  // negative infinity  

Infinity - 1e307;          //Infinity 
Infinity - Infinity;       //NaN
-Infinity * -1;            //Infinity
Infinity * -1;             //-Infinity

To determine if a value is finite there is the isFinite() function.

isFinite(0);                        //true
isFinite(1.7e308);                  //true
isFinite(1.8e308);                  //false
isFinite(Infinity);                 //false
isFinite(-Infinity);                //false
isFinite(Number.MAX_VALUE + 1);     //false
isFinite(Number.POSITIVE_INFINITY); //false
isFinite(Number.NEGATIVE_INFINITY); //false

---

Types

Numbers

NaN

NaN is a special value that represent "Not a Number"

NaN is contagious, any operation involving NaN always returns NaN

Nan + 1 * 2 / 3; //NaN

NaN is not equal to any value, including NaN

NaN === NaN;     //false

To determine if a value is "not a number" there is the isNaN() function.

isNaN(NaN);    //true  - NaN is NaN :)
isNaN(10);     //false - 10 is a number
isNaN("10");   //false - can be converted to number 10
isNaN("blue"); //true  - cannot be converted to a number
isNaN(true);   //false - can be converted to number 1

---

Types

Strings

A string is a sequence of character placed between single or double quotes.

"some characters";
'some characters and numbers 123 5.87';
'1';
"";
"'hello'";
'"hello"';
'hello"; //syntax error - quotes must match

Character Literals

"\n"     // new line
"\t"     // tab
"\b"     // backspace
"\r"     // carriage return
"\f"     // form feed
"\\"     // backslash (`\`)
"\'"     // single quote (`'`)
"\""     // double quote (`"`)
"\xnn"   // character in hexadecimal code `nn` (`n` is a hexadecimal digit).
"\unnnn" // unicode character in hexadecimal code `nnnn` (`n` is a hexadecimal digit).

'he said \'hello\''; //"he said 'hello'"
"he said \"hello\""; //"he said "hello""
'\u03a3';            //"Σ"
'\x41';              //"A"

---

Types

Object

An object is an unordered collection of key/value pairs,
separated by commas ,, placed within curly braces { and }.

The keys are strings, the values can be of any type.

var obj1 = {
  s: "string value", 
  n: 123,
  b: true,
  o: { k: 2 }
};

The keys can optionally be placed in quotation marks.

var obj2 = {
  "s": 'string value',
  'key': 'another value',
  "name with spaces": true
};