javascript
Basics and more...
History
Key ideas
- Load and go delivery
- Loose typing
- Objects as general containers
- Prototypal inheritance
- Lambda
- Linkage through global variables
Data Types
NUMBERS
-
64 bit floating point (Double)
-
NAN
-
String to Number
Quirks
parseInt('06'); //6
parseInt('08'); //0
typeof NaN === 'number' //true NaN === NaN //false
0.1 + 0.2 === 0.3 // false
3.toString();
parseFloat( 'Infinity' ) // returns Infinity Number( 'Infinity' ) // returns Infinity parseInt( 'Infinity' ) // returns NaN
Data Types
STRINGS
- UTF-16 (not even that)
- Immutable
- Compare with ==
- '' or ""
- "hello".length
Bugs
Data Types
BOOLEAN
- true or false
- Falsy: false, 0, "", null, undefined, NAN
- Boolean(value) or !!
Bugs
Number(true); // 1 Number(false); // 0
Boolean(null); // false null == false; // false
Data Types
NULL
A value that isn't anything
UNDEFINED
A value that isn't even that
bugs
typeof null // "object" null instanceof Object // false
undefined = "a"; // possible
Everything else is objects
Duck Typing
When I see a bird that walks like a duck and swims like a duck and quacks like a duck, I call that bird a duck
- James Whitcomb Riley
functions
4 ways to call
- myFunc(1, 2)
- obj.myFunc(1, 2)
- myFunc.call(this, 1, 2) | myFunc.apply(this, [1, 2])
- var obj = new myFunc()
this object
As a method
var foo = {};
foo.someMethod = function(){alert(this);}
As a function
var foo = function(){alert(this);}
foo();
As a constructor
function Foo(){
this.confusing = 'hell yeah';
}
var myObject = new Foo();
With Apply or Call methods
function foo(a,b){alert(this);}
foo.apply('omg',['ah','be']);
closures
function makeFunc(name) {
return function() {
alert(name);
}
}
var myFunc1 = makeFunc("Aconex");
myFunc1();
var myFunc2 = makeFunc("SWAT");
myFunc2();
Use cases
Binding: http://jsfiddle.net/DNH3k/
setTimeout & setInterval: http://jsfiddle.net/nsGNy/4/
Currying: http://jsfiddle.net/xYrqh/ (JSPref)
design patterns
Constructor pattern
Object creation
var newObject = {};
var newObject = Object.create( null );
var newObject = new Object();
Dynamically adding properties
newObject.key = "value"; newObject["key"] = "value";
Constructors: http://jsfiddle.net/c4dBW/
Constructors with prototypes
Module Pattern
using Object Literals
Basic: http://jsfiddle.net/7qDEL/
Import Mixins: http://jsfiddle.net/7qDEL/1/
Disadvantages:
- Headache to change private to public
- New public functions don't have access to private fns
singleton pattern
var mySingleton = (function () {
var instance;
function init() {
var privateRandomNumber = Math.random();
return {
getRandomNumber: function() {
return privateRandomNumber;
}
};
};
return {
getInstance: function () {
if ( !instance ) {
instance = init();
}
return instance;
}
};
})();
// Usage:
var singleA = mySingleton.getInstance();
var singleB = mySingleton.getInstance();
console.log( singleA.getRandomNumber() === singleB.getRandomNumber() ); // true
To note
var a = 1
b = 1;
(function(){
var a = 2
b = 2;
}())
console.log(a);
console.log(b);
function func()
{
return
{
foo: "bar"
};
}
func();
More
var1 == var2 var1 === var2
"1" == true "b" == true
'true' == true !!'true'
Hoisting
function func() {
var a = "String";
function test(){
alert(a);
var a = "Another String";
}
test();
}
func();
function func() {
var a = "String";
function test(){
alert(a);
function a(){alert("test")}
}
test();
}
func();
javascript
By Subin Varghese
javascript
- 135
