robert’swanson’ cnxcorporaon’ - gateway/400 · pdf...

Robert Swanson CNX Corpora1on

Chicago, IL

•  Briefly discuss the history of JavaScript – How did it evolve? What is it used for today?

– Why should I learn it?

•  Review and demysDfy basic JavaScript syntax – Data types, arrays, condiDons, loops –  FuncDons and objects – Along the way, we’ll highlight fundamental similariDes to (and differences from) RPG

•  Learn how to get your hands dirty with JS –  IntroducDon to the browser console – Quick and dirty html file execuDon

•  JavaScript in AcDon – Discuss where JavaScript “fits in” –  See how web pages harness the power of JavaScript frameworks

•  Next Steps – Make yourself a master of this exciDng domain!

•  What is JavaScript?

•  Where JavaScript is Used •  Data Types, Arrays, CondiDons and Loops

•  Fire Up the Browser! •  FuncDons and Objects

•  JavaScript Object NotaDon (JSON)

•  Understanding Asynchronous Apps •  JavaScript Frameworks Explained

•  Wrap-‐Up and Next Steps for Learning

•  “Web 1.0” -‐ staDc HTML and a bunch of links •  Needed a richer user interacDon…

–  Java applets –  LiveScript

•  This front-‐end funcDonality was very popular among website developers

•  And browser makers were eager to deliver…

JavaScript (ECMAScript)

Browser Wars I: 1996-‐2001 •  NetScape vs Microsoe

•  JavaScript vs JScript – Messy –  IncompaDble – Abused –  Bad reputaDon –  “Toy Language”

Microsoe won BW I… •  IE & JScript evoluDon froze •  Standards evolved (ECMA)

•  Other browsers caught up to IE

and “Browser Wars II” began…

• With AJAX, new ways to harness the power of JavaScript were discovered…

•  Today, JavaScript is one of the most popular programming languages in the world

•  Browser makers are falling over each other to make JavaScript performance scream

•  One interpreter on every machine

•  JavaScript has essenDally supplanted Java’s original intent & selling point!

• Worth learning, and you can have fun doing it!

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Client Side HTML CSS JavaScript

Server Side RPG COBOL C Java PHP (etc)

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Common “Web 1.0” applicaDons of JavaScript: •  Object AnimaDon • Mouse-‐over events •  Edit-‐checking •  Text manipulaDon •  Pop-‐up messages •  (etc)


JS Frameworks   Ext JS   Dojo   jQuery   (etc)


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Watch this!!

•  String •  Number

•  Boolean •  Null •  Undefined

“Hello, I’m a text string!”

1, 2.5, -‐30, 4e25, Infinity

true, false

•  No “D Specs” in JavaScript!

•  Use the “var” statement to declare variables var greeting = “Hello, how are you?”;!

•  You can then use “typeof” to interrogate the type typeof greeting;! “string”!

CauDon! Unlike RPG, case maners!

var greeting = “Hello, how are you?”;!typeof greeting;! “string”!

typeof Greeting;! “undefined”!

•  Arrays are idenDfied using [square brackets] •  First element is 0 (unlike RPG, where it’s 1)

var value = [‘first’, ‘second’, ‘third’];!

value[0];! “first” !

value[1];! “second”!

value[3]=‘fourth’;!

Standard “if” statement… RPG: if x>100;! message=‘too much!’;!else;! message=‘looks good.’;!endif;!

JavaScript: if (x>100) {! message=‘too much!’;!} else {! message=‘looks good.’;!}!

JavaScript Jock: message = (x>100) ? ‘too much!’ : ‘looks good.’;!

Comparison Operators

Operator Descrip1on RPG

== Is equal to n/a

=== Is exactly equal to (value and type) =

!= Is not equal to n/a

!== Is not exactly equal to (value and type) <>

> Is greater than >

< Is less than <

>= Is greater than or equal to >=

<= Is less than or equal to <=

&& Logical AND and

|| Logical OR or

Watch for assignment versus comparison when using the equals sign in JavaScript…

Assignment: if (x=‘1’) {}; -‐-‐ this would actually assign a value of ‘1’ to x!

Comparison: x==1; “true” -‐-‐ value converted to numeric then checked

x===1; “false” -‐-‐ value and type are both checked

Generally speaking, best to sDck to ===

JavaScript also supports “truthy” and “falsy”…

“Falsy” values (all evaluate to false if tested):

  false   0 (zero)   “” (empty string)

  Null, undefined, NaN

All other values are considered “truthy”

var x=0; // (or could be x=‘’)!var y=‘hi’; // (or could be y=10)!if (x) {! // this code is not executed! alert(‘x is truthy’);!}!if (y) {! // this code is executed! alert(‘y is truthy’);!}!

switch statement (“SELECT” in RPG)…

RPG: x=1;!select x;! when 0;! message=‘zero’;! when 1;! message=‘one’;! other;! message=‘I dunno!’;!endsl;!

JavaScript: var x=1;!switch (x) {! case 0:! message=‘zero’;! break;! case 1:! message=‘one’;! break;! default:! message=‘I dunno!’;!}!

switch statement (“SELECT” in RPG) – complex…

RPG: x=1;!select;! when x=0;! message=‘zero’;! when x>=1;! message=‘one+’;! other;! message=‘I dunno!’;!endsl;!

JavaScript: var x=1;!switch (true) {! case (x===0):! message=‘zero’;! break;! case (x>=1):! message=‘one+’;! break;! default:! message=‘I dunno!’;!}!

•  JavaScript has four types of loops… – While

– Do-‐while

–  For

–  For-‐in

• While loops are the simplest…

JavaScript var i=0;!while (i<10) {! // do something! i++;!}!

RPG i=0;!dow i<10;! // do something! i+=1;!enddo;!

•  Do-‐While loops are more like “Do UnDl” in RPG

JavaScript var i=0;!do {! // do something! i++;!} while (i<10)!

RPG i=0;!dou i=10;! // do something! i+=1;!enddo;!

•  For loops are the most widely used in JavaScript

JavaScript for (var i=1; i<=10; i++) {! // do something!}!

RPG for i = 1 to 10 by 1;! // do something!endfor;!

•  For-‐in loops are unique to JavaScript •  Niey way to loop through arrays

var alpha=[‘a‘, ‘b‘, ‘c‘, ‘x‘, ‘y‘, ‘z‘];!var result=‘‘, i=0;!for (i in alpha) {! result+= ‘i#‘ + i + ’: ‘ + alpha[i] +’ ... ‘;!}!

result!”i#0: a ... i#1: b ... i#2: c ... i#3:!

RPG: %char(i) !

•  Google Chrome Console –  Control-‐Shie-‐J on Windows

–  Command-‐opDon-‐J on Mac

You can also use Firebug on Firefox, or the integrated console in IE8+, but Chrome seems to be the front-‐runner in the Browser Wars (at least for now)

Let’s try it…

•  Analogous to RPG subprocedures

JavaScript function sum(p1,p2) {! var total = p1+p2;! return total;!}!

RPG p b!d sum pi!d p1 5s 0!d p2 5s 0!d total s 5s 0! /free! total = p1+p2;! return total;! /end-free!p e!

•  FuncDons always return a single value. –  If no “return” specified, then “undefined” is returned implicitly

– MulDple values can be returned as an array

•  “Call a subprocedure” = “Invoke a funcDon”

var result = sum(1,2);!

result! 3 !

•  Anempt to pass extra parms? –  RPG gives a compile-‐Dme error

–  JavaScript just ignores them

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

result! 3 !

•  Pass too few parms? –  RPG produces a run-‐Dme “pointer/parameter error” if program tries to access any of the omined parms

–  JavaScript assigns “undefined” to omined parms, resulDng in strange things if code doesn’t watch for it

sum(1)! NaN

•  “Parms” oeen referred to as “Arguments” • %parms in RPG = arguments.length in JS

function sumOnSteroids() {! var i=0, total=0;! var parmCount = arguments.length;! for (i=0; i<parmCount; i++) {! total += arguments[i];! }! return total;!}!

sumOnSteroids(1,2,3,4,5)! 15

JavaScript also includes a number of pre-‐defined funcDons, such as:

•  parseInt() – parses out a number from a string

•  parseFloat() – same as parseInt but w/ decimals

•  isNaN() – checks if string is Not a Number

•  alert() – quick and dirty message box

•  Almost everything in JavaScript is an “object” –  Strings – Numbers – Arrays –  FuncDons

•  An object is a special kind of data, each with –  ProperDes – Methods

•  JavaScript also lets you create your own objects

Let’s create an object…

var vehicle = {! make: ‘Ford’,! model: ‘F150’,! color: ‘Silver’! };!

vehicle.make! ”Ford”!

properties

You can also have objects within objects…

var vehicle = {! make: ‘Ford’,! model: ‘F150’,! color: ‘Silver’,! engine: {! fuelType: ‘diesel’,! valves: 8!! }! };!

A property with a funcDon is a method…

var vehicle = {! make: ‘Ford’,! model: ‘F150’,! color: ‘Silver’,! honk: function(){ ! alert(‘beep-beep!’);! }! };!

“this” is oeen used to access object properDes

var vehicle = {! make: ‘Ford’,! model: ‘F150’,! color: ‘Silver’,! honk: function(){ ! alert(‘beep-beep goes the ’! +this.make+’ ‘+this.model);! }! };!

Let’s try it…

•  Can go in an .html file (i.e., index.html) •  <script> tag denotes JavaScript secDon <script>!

// JavaScript code goes here!</script>!

•  Script tag can also reference an external .js file <script src=“/myFolder/myApp/app.js”>!

type=“text/javascript”>!<script!

JavaScript

Data Types, Arrays, Conditions, Loops, Functions, Objects….

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JSON

•  Stands for JavaScript Object NotaDon •  Text-‐based data interchange format

•  Similar to XML in theory

•  Lightweight, meaning smaller number of characters

•  Na1ve way of sending data to JavaScript objects




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Customer Master Record Data:

{“CUSNUM”:123456, “CUSNAME”:“HOME DEPOT”}!

JSON string starts with a curly bracket

Field name, which should always be specified within quotes

Field value, which should be in quotes for strings; no quotes for numeric values

Commas separate each name/value pair

Colons separate name and value

Closing curly bracket denotes end of JSON string

Continue specifying name/value pairs until all fields of your record are represented

{“CUSTOMERS”:[ {“CUSNUM”:123456, “CUSNAME”:“HOME DEPOT”}, {“CUSNUM”:987654, “CUSNAME”:“LOWES”}!

]}!

JSON string starts with a curly bracket

Hard bracket opens the array

Comma separates each record

Array name, followed by a colon

Hard bracket closes the array, immediately followed by a curly bracket to end the JSON string

•  JSON is naDve to the front-‐end JavaScript –  Immediately available for use in the program,

i.e.: CUSTOMERS[1].CUSNAME!

•  Back-‐end program (RPG) will need to… –  Receive JSON string from the browser – Deconstruct JSON and place values into variables – Do its thing (business logic) –  Convert output data back into a JSON string –  Send it on to the browser

•  Asnychronous processing gives JavaScript a lot of power (AJAX)

•  It can also be confusing when you’re used to the serial/sequenDal processing world

Classic RPG Green Screen Program…

•  Load subfile records •  Populate header fields •  EXFMT – wait for user

•  Proceed…

Web 1.0 / “Page-‐at-‐a-‐Time”

•  Server constructs HTML, sends page to browser

•  Program terminates

•  AcDon taken by user •  Rinse, Repeat

“Web 2.0” / Asynchronous App

•  JavaScript sent to browser, executes to create page

•  User takes acDon(s) • MulDple programs called asynchronously to respond with data as needed

•  JavaScript code is quite powerful •  Render & manipulate enDre web pages

•  CollecDons of JavaScript widgets and funcDons, aka JavaScript Frameworks, make the whole process much easier

Popular Frameworks include… •  jQuery •  Ext JS •  Dojo •  Prototype • MooTools

•  Countless others

Just about every kind of component imaginable…

•  Frameworks make tricky HTML concepts easier to build by using small pieces of JavaScript

•  For example, a dynamic grid….

HTML for dynamic grid… <div id="example-grid">! <div class="x-panel x-grid-with-row-lines x-panel-default x-grid" style="width:540px;height:200px;" id="gridpanel-1009">! <div class="x-grid-header-ct x-docked x-grid-header-ct-default x-docked-top x-grid-header-ct-docked-top x-grid-header-ct-default-docked-top x-box-layout-ct" style="border-width: 1px; width: 540px; left: 0px; top: 0px;" id="headercontainer-1010">! <div id="headercontainer-1010-innerCt" class="x-box-inner " role="presentation" style="width: 538px; height: 22px;">! <div id="headercontainer-1010-targetEl" style="position: absolute; width: 538px; left: 0px; top: 0px; height: 1px;">! <div class="x-unselectable x-column-header-align-left x-box-item x-column-header x-unselectable-default x-column-header-sort-undefined x-column-header-first x-column-header-sort-DESC" style="border-width: 1px; height: auto; left: 0px; margin: 0px; width: 143px; top: 0px;" id="gridcolumn-1011"><div id="gridcolumn-1011-titleEl" class="x-column-header-inner" style="height: auto; padding-top: 3px;"><span id="gridcolumn-1011-textEl" class="x-column-

// create the grid!var grid = Ext.create('Ext.grid.Panel', {! store: myStore,! columns: [! {text: ‘Author’, flex: 1, dataIndex: 'Author', sortable: true},! {text: ‘Title’, width: 180, dataIndex: 'Title', sortable: true},! {text: ‘Manufacturer’, width: 115, dataIndex: 'Manufacturer',! sortable: true},! {text: ‘Product Group’, width: 100, dataIndex: 'ProductGroup’,! sortable: true}! ],! width: 540,! height: 200!});!

Ext JS for dynamic grid…

•  History of JavaScript • Where JavaScript “fits” in the Web 2.0 World

•  Data types, arrays, condiDons and loops •  How to experiment in browser console

•  Objects and funcDons •  JSON and AJAX and asynchronous apps •  JavaScript Frameworks

•  Read! – Object Oriented JavaScript (Stoyan Stefanov)

– On-‐Line Tutorials (w3schools.com)

•  Experiment! –  Play in your browser & console –  Try out a framework (Valence ideal for RPGers)

•  Consider formal class training –  CNX offers several RPG-‐centric JavaScript courses



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Contact info:

Rob Swanson

[email protected]

312-‐477-‐7473

Download Valence Free!

www.cnxcorp.com/valence

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