/* logic */

var foo = true;

var bar = false;

// lots of things are truthy: '0', 'any string', [] (an empty array), {} (an empty object), any non-zero number

// lots of things are falsy: 0, '' (empty string), NaN, null, undefined

var baz = foo || bar || bim || baz; // logical OR operator || returns the value of the first true comparator (false if none)

var bim = foo && bar && bop && bip; // logical AND operator && returns the value of the last true comparator (false if none)

if (foo) {

// do something if foo is true

} else if (

bar && baz && bim

) {

// do something if bar is true AND foo was false

} else {

// do something if both foo and bar were false

}

/* strings and numbers */

var myNumber = '1';

var foo = parseInt(myNumber) + 2; // 3

var bar = 1 + 2; // 3

/* arrays */

var foo = ['apple', 'orange', 'banana'];

foo.length; // 3

foo[1]; // 'orange'

foo[5] = 'pear'; // assign an element to an index of the array

foo; // ['apple', 'orange', 'banana', undefined, undefined, 'pear']

foo.length; // 6 -- uh oh

var foo = ['apple', 'orange', 'banana'];

foo.push('pear'); // add to an array when last index is not known

foo.length; // 4 -- that's better

foo; // ['apple', 'orange', 'banana', 'pear']

var foo = {

bar : 'baz'

};

/* objects */

var myObject = {

'property' : 'value',

'method' : function() {

alert('hello');

return 'hello';

}

};

myObject.property; // 'value'

myObject.method(); // alerts 'hello'

/* functions */

// defining a function

function myFunction() {

// do stuff

};

var myFunction = function(a, b) {

// do stuff

return (a + b);

};

myFunction();

var foo = 'hello';

var myThing = (function() {

var myFn = function() {

alert(foo);

};

var foo = 'world';

return myFn;

})();

myThing();

// functions can be created and run without ever naming them

(function(arg) { alert(arg); })('hello'); // alerts 'hello'

(function($) {

jQuery('p').text('hello');

})(jQuery);

// functions can receive 0 or more arguments;

// these arguments can be anything, including other functions!

var myFunction = function(a, b) {

alert(a + ' ' + b);

};

var myFunction = function(fn) {

fn(); fn();

};

myFunction(function() { alert('hello'); }); // alerts 'hello' twice

// functions can return things

var myFunction = function(a, b) {

return a + ' ' + b;

};

// functions can even return other functions

var myFunction = function(a, b) {

};

var f = myFunction('hello', 'world');

f(); // alerts 'hello', then alerts 'world'

// functions "close" their variables -- variables defined in a function

// are only available to other objects and functions created inside the function

var myFunction = function() {

var myClosedVariable = 'hello';

};

myFunction();

alert(myClosedVariable); // error; myClosedVariable isn't defined outside the function

var myFunction = function() {

};

alert(myClosedVariable); // error; myClosedVariable isn't defined outside the function

var f = myFunction(); // returns the function created inside myFunction

f(); // this function still has access to myClosedVariable,

// because the function and the variable

// were created in the same scope. this is an example of a closure.

/* another closure example */

// this won't work as expected! all will alert '4'

for (i=0; i<5; i++) {

$('<p>some text</p>').appendTo('body').click(function() {

alert(i);

});

}

// this will work -- put the variable i inside a closure

for (i=0; i<5; i++) {

(function(i){

$('<p>some text</p>')

.appendTo('body').click(function() {

alert(i);

});

})(i);

}

// this will also work, and is a little more clear about what's going on

var createFunction = function(i) {

return function() { alert(i); };

};

for (i=0; i<5; i++) {

$('<p>some text</p>')

.appendTo('body').click(createFunction(i));

}