JavaScript

FrontEnd

• HTML: Basic Structures

• CSS: Style and format

• JavaScript: Hidden Layer-->Logic

function myFunction(){
    document.getElementById("message").innerHTML = "Downloading...";
}

<button onclick = "myFunction()">Download</button>
<p id="message"></p>

Ways to interact:

• Internal JS (loaded based on location in html, has delay sometimes)

<script>
...
</script>

• Extrenal JS (defer and async attributes)

<script src="script.js" defer></script> // defer: JS file load at same time
as HTML loading, No block

• Inline JS handler

<button onclick="myFunction()">Download</button> // Deprecated, Unorganized

JS interpreted:

• JS engine: v8(Chrome), SpiderMonkey(Firefox)

• Node.js encompasses v* within C++ environ to compile without browser (VScode Run with Node.js)

• Online Sandboxes (codepen.io, codesandbox.io)....

• LiveServer-->Local Server

Syntax

• 7 standard data types: numbers, string, boolean, null, undefined, symbol, object

• Dynamically, loosely, typed languages; No need to specify, data type inferred, can change

var userName = "Jack"; // Globally
let userName = "Jill" // Narrow scope: for loop
const interestRate = 4.25 // Final and Global, cannot change

var firstName = "Ru", lastName = "Wang", age = 26; // different data type same line
typeof firstName-->"string"

// Object: unorderd collections of data of PRIMITIVE/REFERENCE types->key: value statements
var TA = {
    firstName: "ALice",
    lastName: "Smith",
    age: 24
}
TA.lastName-->"Smith"
TA["lastName"]-->"Smith"

// Array: can contain elements of different types
var students = ["Andy", "David","Laura"];
students[3] = "Nathan";  // QUESTION HERE
students[4] = 4

// Function: Easy for debugging, recursion
function nameFunc(parameters){
    // Calculate
}

// Anonymous Function: Easy for scope, brevity
var first = function(array){return array[0]};
var first = array => return array[0]; // arrow function

// Function serve as methods with objects
var Report = {
    temp: 77,
    humidity: 64,
    celcius: function(){ // Anonymous funciton, no Name
        reuturn (this.temp-32)*5/9;
    }
}

// Conditionals
if...else
switch
Ternary operator

=== & !== (identical to/not identical to objects, value & type)
== & != (values, not type)

// Any value that is not false, undefined, null, 0, NaN, "" return true
var current = "Alice";
if(current){ // evaluate to true
    ...
}

// Ternary
(condition)? doSth: doSthElse

// for loop
for(initializer; exit-condition; final-expression){
    ...
}

Interacting with User-facing elements

Document Object Model (DOM): Tree structure

Objects: HTML elements,

Property: Value that can get or set, like id of element

Method: An action, like adding or deleting and HTML element

Access HTML elements:

• getElementById(id).innerHTML (also using tag name, class name, CSS selector)

• getElementById(id).src = "HeadShot.png";

• getElementById(id).style.color = "red";

• querySelector(CSS selector)

DOM Events:

onclick, onload, onunload, onchange, onmouserover......

• Inline event handlers

• DOM on-event handler

• Event listener

document.getElementById("convert").onclick = "convertTemp"; // No ()
function convertTemp(){
    ...
}

// Event Listeners
document.getElementById("convert").addEventListener("click", convertTemp); // No ()
function convertTemp(){
    ...
}

// Change multiple elements, all buttons have the same event in this case
document.body.addEventListener("click", event=>{
    if(event.target.nodeName=="BUTTON"){
        console.log("Clicked", event.target.textContent);
    }
});

JSON Data

Definition: Objects are unordered collections of related data or primitive or reference types.

// JSON Objects
{
    "firstName": "dd",
    "role": "Instructor"
}

// JSON Arrays
{"TAs": [
    {"Name": "1", "Year": 2022},
    {"Name": "1", "Year": 2022},
    {"Name": "1", "Year": 2022}
    ]
}

// Use JSON
var text = JSON ARRAY;
obj = JSON.parse(text);
obj.TAs[0].Name, obj.TAs[1].Year

// Request JSON from server
Synchronous OR Asynchronous(Recommanded, produce a callback when data received)

// Callback Function
function greeting(name){ // Synchronous Example
    alert("Hello", name);
}
function processUserInput(callback){
    var name = prompt("Enter your name");
    callback(name);
}
processUserInput(greeting);

XMLHttpRequest() & fetch(): Promise-based method, new
Promise objects represents the eventual completion/failure of an 
async operation and its result value;

// XMLHttpRequest()
var url = "tas.json";
var req = new XMLHttpRequest();
req.open('GET', url, true); // true for async
req.responseType = 'json';

req.onload = function(){
    ...
}
req.send();

// fetch
fetch(url)
    .then(response=>response.json())
    .then(data=>{
        ...
    })
    .catch(error=>console.error(error));
    
// parse and stringify
var tas = parse(JSON); //JSON->JS
var tas = stringify(JS); //JS->JSON 

Working with APIs

Definition: API facilitate the programming of complex functionality

Browser API: fullscreen, screen orientation, vibration....

Third-party API: Google Maps API, Twitter API....

JS interacts with APIs over JS obejcts

<audio src="Haydn_Adagio.mp3" type="audio/mpeg">
</audio>
<button data-playing="false" role="switch" aria-checked="true">
    <span>Play | Pause</span>
</button>

const audioContext = new AudioContext();
const audioElement = document.querySelector('audio');
const track = audioContext.createMediaElementSource(audioElement);
track.connect(audioContext.destination);

playButton.addEventListener('click', function() {
    if (audioContext.state === 'suspended') { 
        audioContext.resume();
    }
    if (this.dataset.playing === 'false') {        
        audioElement.play();this.dataset.playing = 'true';
        console.log("Playing...");    
    } else if (this.dataset.playing === 'true') {        
        audioElement.pause();
        this.dataset.playing = 'false';
        console.log("Stopped..."); 
    }
}, false);
audioElement.addEventListener('ended', () => {    
    playButton.dataset.playing = 'false';
}, false);

Working with Component Library

Bootstrap: npm install bootstrap

Width breakpoints to reorganize the layout

• Container: basic element of layout

<div class="container">
    ...
</div>

<div class="container-fluid">
    ...
</div>

<div class="container-{breakpoint}"> <!-- xs,sm,md,lg,xl -->
    ...
</div>

• Flex box: https://flexbox.malven.co/
• Grids

<div class="row">
    <div class = "col-*-*"></div>
    <div class = "col-*-*"></div>
</div>

<!-- first * is grid class -->

• Content

<img src="..." class="img-fluid">

<table class="table">
    <theadclass="thead-dark">
        <tr>
            <th scope="col">...</th>      
            ...
            
<div class="table-responsive-sm">
    <tableclass="table">  
    ...

Introductiongetbootstrap

Bootstrap 5 Tutorial - An Ultimate Guide for Beginners

Bootstrap 3 Tutorial

Design Thinking

Definition: Approach-->handson, user-centric; Process-->6 phase process: understanding, exploration, materialization

1. Empathize

2. Define

3. Ideation

4. Prototyping

5. Testing

6. Implementation

Empathize

Understand users' need, preference, expectations by studying what they do, think, and feel

Think-alouds

Ask participant to do the task while describing their behavior, and observe their actions with the interface.

Define

• gather: gather findings

• analyze: consolidating, categorizing, distilling

• recommend: translate into insight

Affinity Diagramming: Organize data into clusters based on "affinity"

AKA affinity mapping, collaborative sorting, snowballing

1. Start initial set of categories

2. Sort notes into these categories

3. Add subcategories or consolidate categories as needed

4. Present each category

5. Rank categories in severity, importance, prevalence, frequency

Ideate

Active, creative, highly iterative process for forming ideas for design

Individually or Collaboratively

Idea creationg => Critiquing (2-step process)

IDEO's Rules of Engagement:

1. Defer judgement

2. Encourage wild ideas

3. Build on the ideas of others

4. Stay focused on the topic

5. One conversation at a time

6. Be visual

7. Go for quantity

Sketch: quick and rough drawing that gives a general outline of an idea

• Everyone can sketch

• More effective than words

• Not inhibit exploration

• Disposable

==> Conceptual Design: Abstract characterization of context

Storyboarding: Sequence of visual frames that illustrate user interaction that shape user exp.

Journey Maps: A visualization of the process that a person goes through in order to accomplish a goal

Visual Design

Elements of Design

1. Space: Canvas on which visual elements are placed

   1. Positive: where the subject is positioned

   2. Negative: space surrounding the subject

   3. Negative can be used as positive

2. Line: Most primal design element, divide space, call attention, organize, and make up other

3. Shape: Space outlined by a contour

   1. Geometric

   2. Organic

   3. Abstract

4. Size: Scale, the relative extent of the design elements such as shapes and lines

5. Pattern: Repetition, systematic duplication of design elements such as shapes and lines

6. Texture: Tactile and visual quality of a shape or space, by different color, material, structure

7. Value: The intensity in which a design element is expressed, such as foggy and lightening

Principle of Design

1. Focal Point: Area of visual interest, where the design directs the attention of the viewer first

   1. Color

   2. Large Size

   3. Location of Element

2. Contrast: Juxtaposition of design elements that strikingly differ from each other

3. Balance: Organization of design elements on canvas to provide a sense of balence/imbalance

   1. Symmetry or Asymmetry

4. Movement: Organization of design elements that suggests a particular flow on the canvas

5. Rhythm: Patterned use of design elements that communicate movement or order

6. Perspective: Creating a sense of horizon and movement along the depth axis of canvas

7. Unity: Reflects the holistic consistency in the use of design element

Associated Concepts

• Font: style in which type is created

• Typeface: font family

• Glyph: particular character

Category of typefaces

1. Old-style fonts: "serifs" at the tips of a glyph that taper closer to the tip

2. Modern & slab-serif fonts: Very thin or very thick serifs

3. Sans-serif fonts: Lack the serif at the tips, stroke follow uniform weight

4. Script fonts: Simulate cursive writing where glyph connect with each other at the downstroke

5. Decorative fonts: Specifically to convey a particular context or elicit a particular feeling

Font parameters:

• Style variation: bold, italic, oblique

• Caps: all caps, small caps

• Weight: extra light, light, medium, bold

Color: Visual Perception of light reflecting from object

• Creates emphasis

• Organizes content

• Evokes emotion

Tints: Add White to color

Shades: Add Black to color

Hue: Standard color: red, yellow, blue

Color Palettes

• Analogous: Nearby colors on color wheel

• Complementary: Opposite colors on color wheel

• Split-Complementary: One color on 1 side, 2 colors on opposite side

• Triadic: 3 distinct colors

• Monochromatic: One Hue, adjust gray scale

• Achromatic: Only use gray scale colors

Color Vision Deficiencies

• Intensity vs Hue for emphasis

• Size of colored element

• Proximity of similar colors

Run color blindness tests on your websites - gHacks Tech NewsgHacks Technology News

Images

Photograph, illustrations, 3D art, etc... convey rich information or context

• Raster Graphic: Conventional, bitmap, pixels, zoom in-->blurry

• Vector Graphic: Computer generated, flexible in scaling