JavaScript Basics And DOM Manipulation

Siarhei Barysiuks.barysiuk@sam-solutions.net

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JavaScript Primitive Types

• number• string• boolean• null• undefined

There are five primitive data types in JavaScript:

Everything that is not a primitive is an object.

JavaScript: Primitive types

Numbers

JavaScript: Primitive types: Numbersvar n1 = 1;out(typeof n1); var n2 = 1.5;out(typeof n2);

var n3 = 0100;out(typeof n3);out (n3);

var n4 = 0xFF;out(typeof n4);out(n4);

>> "number"

>> "number"

>> "number">> 64

>> "number">> 255

JavaScript: Primitive types: Numbers

var n5 = 1e1;out(typeof n5);out(n5); var n6 = 2e+3;out(typeof n6);out(n6);

var n7 = 2e-3;out(typeof n7);out(n7);

>> "number">> 10

>> "number">> 2000

>> "number">> 0.002

JavaScript: Primitive types: Numbers

var n8 = Infinity;out(typeof n8);out(n8);

var n9 = 1e309;out(typeof n9);out(n9);

var n10 = 6/0;out(typeof n10);out(n10);

var n11 = -1*Infinity;out(typeof n11);out(n11);

>> "number">> Infinity

>> "number">> Infinity

>> "number">> Infinity

>> "number">> -Infinity

JavaScript: Primitive types: Numbers

var n12 = NaN;out(typeof n12);out(n12);

var n13 = 10 * "string";out(typeof n13);out(n13);

var n14 = 1 + 1 + NaN;out(typeof n14);out(n14);

>> "number">> NaN

>> "number">> NaN

>> "number">> NaN

{ }NaN - Not a Number.

Strings

JavaScript: Primitive types: Strings

var s1 = "some string";out(typeof s1);

var s2 = 'a';out(typeof s2);

var s3 = "10";out(typeof s3);

>> "string"

>> "string"

>> "string"

{ }Any value placed between single or double quotes is considered a string.

JavaScript: Primitive types: Stringvar s41 = "one";var s42 = "two"var s43 = s41 + s42;out(s43); var s51 = "10";out(typeof s51);var s52 = s51 * 5;out(s52);out(typeof s52); var s6 = "1";out(typeof s6);out(++s6);out(typeof s6); var s7 = "some string 1";var s71 = s7 * 1;out(typeof s7);out(s71);out(typeof s71);

>> "onetwo"

>> "string"

>> 50>> "number"

>> "string">> 2>> "number"

>> "string">> NaN >> "number"

Boolean

JavaScript: Primitive types: Boolean

var b1 = false;out(typeof b1);

var b2 = "some string";var b21 = !b2;var b22 = !!b2;out(typeof b2);out(b21);out(typeof b21);out(b22);out(typeof b22);

>> "boolean"

>> "string">> false>> "boolean">> true>> "boolean"

JavaScript: Primitive types: Boolean

var b31 = "";var b32 = null;var b33 = false;var b34 = NaN;var b35 = undefined;var b36 = 0;

if ( !b3* ) { //executes this section //... }}

All values become true when converted to a boolean, with the exception of the six falsy values:

JavaScript: Primitive types: Boolean

Some interesting comparison operations:

!= ==Non-equality comparison:

Returns true if the operands are not equal to each other.

Equality comparison: Returns true when both operands are equal. The operands are converted to the same type before being compared.

!==Non-equality comparison without type

conversion: Returns true if the operands are not equal OR they are different types.

===Equality and type comparison:

Returns true if both operands are equal and of the same type.

JavaScript: Primitive types: Boolean

Some interesting comparison operations:

var b4 = 2!="2";var b41 = 2=="2"; var b42 = 2!=="2";var b43 = 2==="2";

>> false>> true >> true>> false

Null & Undefined

JavaScript: Primitive types: Null

var nl1 = null;out(typeof nl1);out(nl1);

var nl2 = 1 + null;out(nl2);

var nl3 = 1*null;out(nl3);

>> "object">> null

>> 1

>> 0

JavaScript: Primitive types: Undefined

var u1 = {}; //try to access to nonexistent //field of the objectout(typeof u1.nonexistent);out(u1.nonexistent); var u2 = 1 + undefined; out(u2); var u3 = 1 * undefined;out(u3);

>> undefined>> undefined

>> NaN

>> NaN

Arrays

JavaScript: Arrays

var a = [1,2,3];out(typeof a);out(a);out(a[0]);out(a[5]); a[5] = "some string";out(a); delete a[2];out(a); delete a[5];out(a);

>> "object">> [1,2,3]>> 1>> undefined a[5] = "some string";>> [1,2,3, undefined, undefined,"some string"]

>> [1,2, undefined, undefined, undefined, "some string"] >> [1,2, undefined, undefined, undefined, undefined]

JavaScript: Arrays

var a2 = [[1,2,3],["string1","string2",3]];out(a2[0]);out(a2[1]); var a3 = "one";out(typeof a3);out(a3[0]);out(typeof a3[0]);out(a3[1]);

>> [1,2,3]>> ["string1","string2",3]

>> "string" >> "o">> "string">> "n"

Questions?

Functions

JavaScript: Functions

The power of functions. Where most programming languages have a special syntax for some object-oriented features, JavaScript just uses functions.

function sum(a,b) { return a + b;}

var r1 = sum(1,1); >> 2

JavaScript: Functions: ParametersA function may not require any parameters, but if it does and you forget to pass them, JavaScript will assign the value undefined to the ones you skipped.

function sum(a,b) { return a + b;}

var r2 = sum(1);

function sum(a,b) { return a + b;}

var r3 = sum(1,2,3,4,5);

r2 >> NaN r3 >> 3

{ }1 + undefined = NaN

JavaScript: Functions: Parameters

function sumAll() { var result = 0; for(var i=0,length=arguments.length;i<length;i++){ result+=arguments[i]; } return result;}

var r4 = sum(1,2,3,4,5,6,7);

arguments is array of parameters which function accepts.

r4 >> 28

JavaScript: Functions: ScopeVariables in JavaScript are not defined in a block scope, but in a function scope.

This means that • if a variable is defined inside a function, it's not visible outside of the function. • if a variable defined inside an if or a for code block is visible outside the code block.

function func() { var a = "local"; if(true) { out(a); var a2 = "local-if"; out(a2); } out(a); out(a2);}

>> "local"

>> "local-if"

>> "local">> "local-if"

JavaScript: Functions: Function literal notation

var func3 = function(a,b) { return a*b;

};

var f3 = func3;

Functions are like any other variable.

typeof func3 >> "function"typeof f3 >> "function" func3(2,2) >> 4 f3(3,3) >> 9

JavaScript: Functions: Built-in constructor

var func6 = new Function("a,b","return a+b;");func6(2,2) >> 4

}Do not use the Function() constructor. As with eval() and setTimeout(),always try to stay away from cases where you pass JavaScript code as a string. {

JavaScript: Functions: Anonymous Functions

(function(a,b) { out(a-b);})(5,3);

•You can pass an anonymous function as a parameter to another function. •You can define an anonymous function and execute it right away.

function execute(func) { out(func());}

execute(function() {return "hello, i'm anonymous function!";

});

>> "hello, i'm anonymous function!"

>> 2

JavaScript: Functions: Callback Functions

function info(){ return "this is info function.";}

function execute(func) { out(func());}

execute(function() { return "hello, i'm anonymous function!";});

execute(info);

anonymous callback function

callback function

JavaScript: Functions: Inner functions

function funcTop() {

var a = function() { out("innerFunction: do some work..."); }

out("funcTop: do some work..."); a(); }

define function

call function

•Keep the global namespace clean•Privacy

JavaScript: Functions: Scope

var r5 = "global";

function func1() { out(r5); var r5 = "local"; out(r5);}

func1();

var r5 = "global";

function func1() { out(r5);}

func1();

r5 >> undefinedr5 >> "local"

r5 >> "global"

JavaScript: Functions: Lexical scopeIn JavaScript, functions have lexical scope. This means that functions create their environment (scope) when they are defined, not when they are executed.

function func4() { var v = 1; return func5();};

function func5() { return v;

};

out(func4());

function func41() {var v = 1;

return (function() { return v;

})();};

out(func41());

>> ReferenceError: v is not defined >> 1

JavaScript: Functions: Lexical scope

Global

F

Nab

c

var a;//..function F() { var b; //.. function N() { var c; //.. }}

JavaScript: Functions: Lexical scope

Global

F

N

ab

c

var a;var N;//..function F() { var b;

//..N = function () {

var c; //.. }}

Questions?

Objects

JavaScript: Objects

var obj = { prop:1, prop2:"string", "unusual-prop":"value", 'WTF?$#!@$':{ a:"a-val" }, array: [1,2,3]};

JavaScript uses •arrays to represent indexed arrays •objects to represent associative arrays (hashes)

typeof obj >> objectobj.prop >> obj["unusual-prop"] >> "value" obj['WTF?$#!@$'].a >> "a-val"obj.array >> [1,2,3]obj["array"] >> [1,2,3]

JavaScript: Objects : Defining a new property

var obj = { prop:1, prop2:"string", "unusual-prop":"value", 'WTF?$#!@$':{ a:"a-val" }, array: [1,2,3]};

obj.prop3 >> undefinedobj.prop3 = "value3";obj.prop3 >> "value3"

JavaScript: Objects : PassingPassing objects by reference.

var obj1 = { a:"val-a"};

var obj2 = obj1; obj1.a >> "val-a"obj2.a >> "val-a" obj2.a = "val-a2"; obj1.a >> "val-a2"obj2.a >> "val-a2"

//..var obj3 = { a:"val-a"};

obj1===obj2 >> trueobj1===obj3 >> false

JavaScript: Objects: Functions

var dog = { name: "Bobik", talk: function() { return "Woof, woof!"; }, sayName: function() { return this.name; }};

dog.name >> "Bobik" dog.talk() >> "Woof, woof!"dog.sayName() >> "Bobik"

JavaScript: Objects: Constructor

function Cat(/*String*/ name) { this.name = name; this.talk = function() { return "I'm "+this.name+". Mrrr, miaow!"; }}

var cat = new Cat("Barsik");

typeof cat >> objectcat.name >> "Barsik"cat.talk() >> "I’m Barsik. Mrrr, miaow!"

JavaScript: Objects: Constructor

function Cat(/*String*/ name) { this.name = name; this.talk = function() { //... }}

var cat2 = Cat("Barsik");

call without new

typeof cat2 >> undefinedcat2.name >> TypeError: cat2 has no properties

this refers to the global object window

window.name >> "Barsik"

JavaScript: Objects: Constructor

var cat = new Cat("Barsik");

var constr = cat.constructor;var cat3 = cat.constructor("Murzik");

When an object is created, a special property is assigned to it behind the scenes — the constructor property.

constr >> function Cat(name) { .... }cat3.talk() >> "I’m Murzik. Mrrr, miaow!"

JavaScript: Objects: call and applyTwo useful methods of the function objects are call() and apply().

They allow your objects to borrow methods from other objects and invoke them as their own.

var cat = new Cat("Barsik");//..var cat4 = {name:"Chernysh"};

cat.talk.call(cat4/**, param1, param2, ... **/) >> "I’m Chernysh. Mrrr, miaow!"cat.talk.apply(cat4/**, [param1, param2, ...] **/) >> "I’m Chernysh. Mrrr, miaow!"

JavaScript: Objects: instanceofinstanceof operator tests if an object was created with specific constructor function.

var cat = new Cat("Barsik");var o = {};

cat instanceof Cat >> truecat instanceof Object >> true

o instanceof Object >> trueo instanceof Cat >> false

Questions?

Prototype

JavaScript: Prototype: Intro

• not be confusing things, it’s not prototype.js library• JavaScript has prototype-based object model

JavaScript: Prototype: prototype property

function Cat(/*String*/ name) {this.name = name;

this.talk = function() { return "I'm "+this.name+". Mrrr, miaow!"; }};

Cat.prototype >> {} (object) for(var i in Cat.prototype) { i+":"+Cat.prototype[i] >> ${propName}:${propValue}}

the way how enumerate all properties in an object

JavaScript: Prototype: Adding properties

var cat = new Cat("Barsik");Cat.prototype.animal = "cat";

Cat.prototype >> {animal: "cat"}cat.animal >> "cat"

Cat.prototype.seeADog = function() { return "I'm "+this.name+". Sshhhhhhh!";} cat.seeADog() >> "I'm Barsik. Sshhhhhhh!";

Adding methods and properties to the prototype property of the constructor function is another way to add functionality to the objects this constructor produces.

JavaScript: Prototype: Adding properties

var cat = new Cat("Barsik");Cat.prototype.animal = "cat";

Cat.prototype = { animal: "cat", seeADog : function() { return "I'm "+this.name+". Sshhhhhhh!"; }}

cat.animal >> "cat"cat.seeADog() >> "I'm Barsik. Sshhhhhhh!";

The same result as in the previous example ...

Overriding the prototype completely

JavaScript: Prototype: Changing prototype

var cat = new Cat("Barsik");var cat2 = new Cat("Murzik");

Cat.prototype.animal = "cat";

cat.animal >> "cat"cat2.animal >> "cat"

Cat.prototype.animal = "dog";

cat.animal >> "dog"cat2.animal >> "dog"

Changing the prototype for all Cat instances

JavaScript: Prototype: Own props vs. prototype ones

function Gadget(/*String*/ name) { this.name = name;}

var iphone = new Gadget("iPhone");

Gadget.prototype.name = "none";

iphone.name >> "iPhone"delete iphone.name;iphone.name >> "none"

JavaScript: Prototype: Extending built-in objectsYeah, it’s possible...

String.prototype.getSecondLetter = function() { return this[1];} var str = "hello!";str.getSecondLetter() >> "e"

... but be careful.

Inheritance

JavaScript: Inheritance: Prototype Chaining Examplefunction Shape() { this.name = "Shape"; this.getName = function() { return this.name; }}; function TwoDShape() { this.name = "2DShape";}; function Triangle(/*Number*/ side, /*Number*/ height) { this.side = side; this.height = height; this.name = "Triangle"; this.getArea = function() { return this.side * this.height / 2; }}

JavaScript: Inheritance: Prototype Chaining ExampleTwoDShape.prototype = new Shape();Triangle.prototype = new TwoDShape(); TwoDShape.prototype.constructor = TwoDShape;Triangle.prototype.constructor = Triangle;

var t = new Triangle(10,4);out(t.getArea());out(t.getName());

out(t.constructor);

out(t instanceof Triangle);out(t instanceof TwoDShape);out(t instanceof Shape);out(t instanceof String);

out(Triangle.prototype.isPrototypeOf(t));out(TwoDShape.prototype.isPrototypeOf(t));out(Shape.prototype.isPrototypeOf(t));out(String.prototype.isPrototypeOf(t));

var shape = new Shape();out(shape.getName());

>> 20>> Triangle

>> function Triangle(side,height){...}

>> true>> true>> true>> false

>> true>> true>> true>> false

>> Shape

JavaScript: Inheritance: Shared Properties

function Obj() { this.text = "Hello this world!";};

Move shared properties to prototype.

function Obj() {};Obj.prototype.text = "Hello this world!";==

But how about memory usage?

JavaScript: Inheritance: Some profiling results

Activity Monitorprototype propertythis. property

v. 3.0.1 Mac OS

JavaScript: Inheritance: Inheriting the prototype only function Shape() {}Shape.prototype.name = "Shape";Shape.prototype.getName = function() { return this.name;}; function TwoDShape() {}TwoDShape.prototype = Shape.prototype;TwoDShape.prototype.constructor = TwoDShape;TwoDShape.prototype.name = "2DShape"; function Triangle(/*Number*/ side, /*Number*/ height) { this.side = side; this.height = height;}

Triangle.prototype = TwoDShape.prototype;Triangle.prototype.constructor = Triangle;

Triangle.prototype.name = "Triangle";Triangle.prototype.getArea = function() { return this.side * this.height / 2; }

JavaScript: Inheritance: Inheriting the prototype only

var t = new Triangle(10,4);out(t.getArea());out(t.getName());

out(t.constructor);

out(t instanceof Triangle);out(t instanceof TwoDShape);out(t instanceof Shape);out(t instanceof String);

out(Triangle.prototype.isPrototypeOf(t));out(TwoDShape.prototype.isPrototypeOf(t));out(Shape.prototype.isPrototypeOf(t));out(String.prototype.isPrototypeOf(t));

var shape = new Shape();out(shape.getName());

>> 20>> Triangle

>> function Triangle(side,height){...}

>> true>> true>> true>> false

>> true>> true>> true>> false

>> Triangle

Questions?

Even more...

JavaScript: General: Even more...

• Math - mathematical constants and functions.• Date - working with dates.• RegExp - regular expressions.

See more info on

www.developer.mozilla.org

JavaScript: General: Exception handling

try { iDontExist();}catch(e){ //process error here

out(e);}finally { //do some work here}

>> ReferenceError: iDontExist is not defined

JavaScript: General: Exception handling

• EvalError• RangeError• ReferenceError• SyntaxError• TypeError • URIError• Your own with new Error([message[, fileName[, lineNumber]]])

Questions?

Document Object Model

DOM: Introduction

The Document Object Model is an API for HTML and XML documents. It provides a structural representation of the document, enabling you to modify its content and visual presentation. Essentially, it connects web pages to scripts or programming languages.

The Document Object Model, a language-neutral set of interfaces.

DOM: Chair Construction Analogy

Model API

DOM: HTML document<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"

"http://www.w3.org/TR/html4/strict.dtd"><html> <head> <meta http-equiv="Content-Type"

content="text/html; charset=UTF-8" /> <title>ToDo list</title> </head> <body> <div>What I need to do.</div> <p title="ToDo list">My list:</p> <ul> <li>Finish presentation</li> <li>Clean up my home.</li> <li>Buy a bottle of milk.

(May be beer will be better?;)</li>

</ul> </body></html>

DOM: Finding elements

<input type="text" id="message" value="Messages goes here..."/>

...

var msgInput = document.getElementById("message");

<ul id="list"> <li>Item 1</li> <li>Item 2</li> <li>Item 3</li></ul>

...

var items = document.getElementsByTagName("li");

element or null

array of element or an empty array

<p title="ToDo list">My tasks</p>

DOM: Elements

Node types:

an HTML element - 1an attribute - 2a text node - 3

DOM: Element attributes

• nodeName• nodeValue• nodeType• parentNode• childNodes• firstChild• lastChild• previousSibling• nextSibling• attributes• ownerDocument

DOM: Manipulating the DOM

var item = document.createElement("li");var text = document.createTextNode(message);item.appendChild(text);

parent.appendChild(item);

parent.insertBefore(someNode, item);

parent.innerHTML = parent.innerHTML + ("<li>"+message+"</li>");

parent.removeChild(item);

DOM: Event Handlers

var addBtn = document.getElementById("addBtn");var list = document.getElementById("list");if(addBtn) { addBtn.onclick = function(event) {

console.log(event);var value = msgInput.value;

if(value) { createListEntry(list,value); } else { alert("Message is empty!"); } }}

DOM: Events: Capturing and Bubbling

var addBtn = document.getElementById("addBtn");

//...

addBtn.addEventListener('click', function(){ //code goes here},false);

addBtn.attachEvent('click', function(){ //code goes here});

DOM: Events: Capturing and Bubbling

DOM: Let’s see an exampleToDos application

• adding tasks• deleting tasks• reordering tasks• no backend support

Very early alpha ;)

Questions?