JavaScript in Depth

Svetlin NakovTelerik

Corporationwww.telerik.com

Table of Contents What we know so far

JavaScript syntax JavaScript operators JavaScript Data Types JavaScript Pop-up boxes If and switch, loops functions

What is an object?2

Table of Contents (2) Built-in JavaScript objects

(common) Boolean Number Array String Date RegExp Function Object

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Table of Contents (3) Built-in JavaScript objects

(uncommon) Typed arrays Errors JSON Math Infinity NaN undefined

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Table of Contents (4) Enter the DOM

Difference between JS and DOM DOM objects Querying the DOM Traversing the DOM Manipulation Events

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Table of Contents (5) Browser differences Feature detection Shims, shivs Polyfills JavaScript libraries Closures Module pattern

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What we know so far?

Just a recap

Built-in Objecta.k.a. language features

Boolean Boolean It’s either true or false There isn’t much to it Just know that:

Use x = Boolean(false), or x = false instead

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x = new Boolean(false)if (x) { // this code will execute}

Number Doesn’t do much either

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Array One of the favourite data structures in

JS Supports instance and literal syntax Array properties

length – that’s it Array methods

Mutators: pop, push, reverse, shift, sort, splice, unshift

Accessors: concat, join, slice, indexOf*, lastIndexOf*

Iterators*: filter, forEach, every, map, some, reduce

* = not yet fully supported

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Array Mutators

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var arr = [1,2,3];

arr.pop() // => 3 (last element), arr=[1,2]

// Array.push(element)arr.push(4) // => 3 (arr.length), arr=[1,2,4]

arr.reverse() // => [4,2,1], arr=[4,2,1]

arr.shift() // => 4 (first element), arr=[2,1]

// Array.unshift(element)arr.unshift(5) // => 3 (arr.length), arr=[5,2,1]

arr.sort() // => [1,2,5], arr=[1,2,5]

// Array.splice(index, howMany[, element1[,...[,element2]]])arr.splice(1,1,6,7,8) // =>[2] (removed), arr=[1,6,7,8,5]

Array Accessors

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var arr = [1,2,3];var arr1 = [4,5,6];

arr.concat(arr1) // => [1,2,3,4,5,6], arr=[1,2,3]

// arr.join(separator)arr.join(“ | ”) // => “1 | 2 | 3”, arr=[1,2,3]

// arr.slice(begin[, end])arr.slice(0,1) // => [1,2], arr=[1,2,3]

arr.indexOf(1) // => 0arr.indexOf(5) // => -1

arr.push(1) // arr=[1,2,3,1]arr.lastIndexOf(1) // => 3arr.lastIndexOf(5) // => -1

String For strings or a sequence of characters

(array wise) Supports instance and literal syntax Supports array like accessing e.g.

string[0] String properties

length String methods

charAt, concat, indexOf, lastIndexOf, match, replace, search, slice, split, substr, substring, toUppserCase, toLowerCase, trim*, trimLeft*, trimRight*

Just to name a few14

String Methods

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var str = “Hello, World!”;

str.charAt(1) // => “e”str.concat(“!!”) // => “Hello, World!!!”

str.indexOf(“o”) // => 4str.indexOf(“x”) // => -1str.lastIndexOf(“o”) // => 8str.lastIndexOf(“x”) // => -1

str.replace(“Hello”, “Goodbye”) // “Goodbye, World!”

str.split(“ ”) // => [“Hello,”, “World!”]

// str.substr(start[, length])str.substr(0,4) // => “Hell”// str.substring(indexA[, indexB])str.substring(0,4) // => “Hell”

Date Creates Date instances which let you work with dates and times.

Only instance syntax Few “static” methods Many instance methods

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RegExp Deals with regular expression Supports literal and instance syntax RegExp properties

global ignoreCase multiline lastIndex

RegExp methods exec test

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Function The function is an object too In case you wander:

new Function ([arg1[, arg2[, ... argN]],] functionBody);

new Function("a", "b", "return a + b"); Function methods (of note)

apply bind call toSource, toString

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Function Methods

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function doStuff(a,b,c) { alert(this); alert(a + b + c);}

doStuff(1,2,3) // => [Object Window], 6

// function.call(thisArg[, arg1[, … [,argn]]])doStuff.call(“Ola”,2,3,4) // => “Ola”, 9

// function.apply(thisArg[, argsArray])doStuff.apply(“Ola”,[2,3,4]) // => “Ola”, 9

Object Surprisingly, it had few things Now it’s getting better Methods*:

Object creation: create

Object properties: hasOwnProperty, definePoperty,

defineProperties, keys Sealing

seal, freeze, isSealed, isFrozen

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Document Object Model

(DOM)

Document Object Model (DOM)

Every HTML element is accessible via the JavaScript DOM API

Most DOM objects can be manipulated by the programmer

The event model lets a document to react when the user does something on the page

Advantages Create interactive pages Updates the objects of a page without

reloading it22

DOM Nodes The DOM hierarchy consists of nodes

Each node has a type Important types:

Node.ELEMENT_NODE == 1 Node.TEXT_NODE == 3 Node.COMMENT_NODE == 8 Node.DOCUMENT_NODE == 9

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DOM Nodes Types Other types:

Node.ATTRIBUTE_NODE == 2

Node.CDATA_SECTION_NODE == 4

Node.ENTITY_REFERENCE_NODE == 5

Node.ENTITY_NODE == 6

Node.PROCESSING_INSTRUCTION_NODE == 7

Node.DOCUMENT_TYPE_NODE == 10

Node.DOCUMENT_FRAGMENT_NODE == 11

Node.NOTATION_NODE == 12 24

Querying the DOM Three general approaches:

Query a specific element Query a collection of elements Built in collections

Some methods are applied to document only

Some could be applied to elements

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Querying the DOM (2)

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var header = document.getElementById( “header” );// => DOMElement or Null if not found

var inputs = document.getElementsByName( “choises” );// => NodeList with 0 or more elements

var divs = document.getElementsByTagName( “div” );// => NodeList with 0 or more elements

var popups = document.getElementsByClassName( “popup” );// => NodeList with 0 or more elements

var links = document.links;// => NodeList with 0 or more elements

var header1 = document.querySelector( “#header” );var popups2 = document.querySelectorAll( “.popup” );

Querying the DOM (3)

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var section = document.getElementById( “section” );

var divs = section.getElementsByTagName( “div” );

var popups = section.getElementsByClassName( “popup” );

var header = section.querySelector( “#header” );var popups2 = section.querySelectorAll( “.popup” );

Some methods are applied to document only

Some could be applied to elements

Traversing the DOM

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You are somewhere in the DOM and you need to get elsewhere

Methods for adjacent nodes Methods for children collection

Traversing the DOM (2)

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// Going UPnode.parentNode // parent node or null if node is document

// Going DOWNnode.childNodes // collection of all the child nodesnode.fistChild // first node or null if nonenode.lastChild // last node or null if none

// Going LEFTnode.previousSibling // preceding node or null if none

// Going RIGHTnode.nextSibling // succeeding node or null if none

Accessing Elements through the DOM Tree –

Example

Warning: may not return what you expected due to Browser differences 30

var el = document.getElementById('div_tag');alert (el.childNodes[0].value);alert (el.childNodes[1]. getElementsByTagName('span').id);…<div id="div_tag"> <input type="text" value="test text" /> <div> <span id="test">test span</span> </div></div> accessing-elements-

demo.html

DOM Manipulation Once we access an element, we can read and write its attributes

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function change(state) { var lampImg = document.getElementById("lamp"); lampImg.src = "lamp_" + state + ".png"; var statusDiv = document.getElementById("statusDiv"); statusDiv.innerHTML = "The lamp is " + state";}…<img src="test_on.gif" onmouseover="change('off')" onmouseout="change('on')" />

DOM-manipulation.html

Common Element Properties

Most of the properties are derived from the HTML attributes of the tag E.g. id, name, href, alt, title, src,

etc… style property – allows modifying the CSS styles of the element Corresponds to the inline style of

the element Not the properties derived from

embedded or external CSS rules Example: style.width, style.marginTop, style.backgroundImage

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Common Element Properties (2)

className – the class attribute of the tag

innerHTML – holds all the entire HTML code inside the element

Read-only properties with information for the current element and its state tagName, offsetWidth, offsetHeight, scrollHeight, scrollTop, nodeType, etc…

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DOM Events

DOM Events JavaScript can register event handlers Events are fired by the Browser and

are sent to the specified JavaScript event handler function

Can be set with HTML attributes (legacy):

Can be accessed through the DOM (legacy):

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<img src="test.gif" onclick="imageClicked()" />

var img = document.getElementById("myImage");img.onclick = imageClicked;

DOM Events (2) Can be accessed through the DOM (standard):

“onclick” vs “click” Clicking on one element, clicks all the way up the DOM!

False makes element event to fire first

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var img = document.getElementById("myImage");img.addEventListiner(“click”, imageClicked, false)

The HTML DOM Event Model (3)

All event handlers receive one parameter It brings information about the

event Contains the type of the event

(mouse click, key press, etc.) Data about the location where the

event has been fired (e.g. mouse coordinates)

Holds a reference to the event sender E.g. the button that was clicked

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The HTML DOM Event Model (4)

Holds information about the state of [Alt], [Ctrl] and [Shift] keys

Some browsers do not send this object, but place it in the document.event

Some of the names of the event’s object properties are browser-specific

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Common DOM Events Mouse events:

onclick, onmousedown, onmouseup onmouseover, onmouseout, onmousemove

Key events: onkeypress, onkeydown, onkeyup Only for input fields

Interface events: onblur, onfocus onscroll 39

Common DOM Events (2)

Form events onchange – for input fields onsubmit

Allows you to cancel a form submission

Useful for form validation Miscellaneous events

onload, onunload Allowed only for the <body> element Fires when all content on the page

was loaded / unloaded40

onload Event – Example onload event

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<html><head> <script type="text/javascript"> function greet() {alert("Loaded.");} document.body.addEventListener(“load”, greet, false) </script></head><body></body></html>

Debugging JavaScript

Debugging JavaScript Modern browsers have JavaScript console where errors in scripts are reported Errors may differ across browsers

Several tools to debug JavaScript Microsoft Script Editor

Add-on for Internet Explorer Supports breakpoints, watches JavaScript statement debugger; opens

the script editor 43

Firebug Firebug – Firefox add-on for debugging JavaScript, CSS, HTML Supports breakpoints, watches,

JavaScript console editor Very useful for CSS and HTML too

You can edit all the document real-time: CSS, HTML, etc

Shows how CSS rules apply to element

Shows Ajax requests and responses Firebug is written mostly in

JavaScript44

Firebug (2)

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JavaScript Console Object

The console object exists only if there is a debugging tool that supports it Used to write log messages at

runtime Methods of the console object:

debug(message) info(message) log(message) warn(message) error(message)

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Browser differences

Every browser for itself

Browser differences The landscape today:

Desktop 5 major desktop browsers 4 major desktop rendering engines

Mobile 4 major mobile browsers 4 major mobile rendering engines

Platform = browser + OS Make the math

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Feature detection Feature detection Shims, shivs Polyfills JavaScript libraries Clojures Module pattern

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Shims, shivs What is feature detection Shim – a compatibility

workaround Shiv – a shim that ends with a “v”

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Polyfills Polyfill, or polyfiller, is a piece of

code (or plugin) that provides the technology that you, the developer, expect the browser to provide natively

Flattening the API landscape if you will

A shim that mimics a future API providing fallback functionality to older browsers

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Closures A "closure" is an expression

(typically a function) that can have free variables together with an environment that binds those variables (that "closes" the expression)

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(function() {

// do stuff here // what happens in closure stays in closure // unless exposed

})()

Module pattern Basically, an implementation of

closure

or

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var Module = (function() { // Do magic stuff here // Don’t forget to return return { … } // some object})()

(function() { // Do magic stuff here // Don’t forget to return window.Module = { … } // some object})()

JavaScript libraries A JS library may:

Abstract common work: Traversing / manipulating DOM Ajax related Animations

Normalize browser differences trough shims

Have syntactic sugar for easier coding

Have a module factory 54

JavaScript in Depth

Questions? ?

?? ? ??

?? ?

?

Exercises1. Create an HTML page that has two text

fields (first name and last name) and a button. When the user clicks the button, a message should show the text in the text fields followed by the current time.

2. Create a Web page that asks the user about his name and says goodbye to him when leaving the page.

3. Modify the previous HTML page to have a text field for email address and on clicking the button check if the email is valid (it should follow the format <something>@<host>.<domain>).

4. Create a Web page that shows 20 <div> elements with random location, size and color.

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Exercises (2)5. Create a drop-down menu

Use table for the main menu blocks Use hidden <DIV> elements (display: none; position:absolute; top:30px)

Use JavaScript and onmouseover and onmouseout event to change display: none/block

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Exercises (3)6. Create a DTHML page that has <div>

containing a text that scrolls from right to left automatically Use setInterval() function to move

the text at an interval of 500 ms Use overflow:hidden for the <div> Use scrollLeft and scrollWidth

properties of the <div> element

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