JavaScript and Jupyter references

JavaScript is the most important language you need to learn as a frontend developer. Jupyter Notebooks is a convenient way to learn portions of the language without the overhead of creating a full Website. Jupyter Notebooks have ChatGPT plugins to assist with design and troubleshooting problems. This Notebook has colors on HTML pages that were designed with a dark mode background.

output using HTML and CSS

Multiple cells are used to setup HTML in this lesson. Many of the JavaScript cells will use the output tag(s) to write into the HTML that has been setup.

%%html
<html>
    <head>
        <style>
            #output {
                background-color: #353b45;
                padding: 10px;
                border: 3px solid #ccc;
            }
        </style>
    </head>
    <body>
        <p id="data" hidden>
        </p>
        <div id="output">
            Hello!
        </div>
    </body>
</html>
Hello!

other outputs explored

There are several ways to ouput the classic introduction message: “Hello, World!”

%%js // required to allow cell to be JavaScript enabled

console.log("JavaScript/Jupyter Output Intro");

// Browser Console output; debugging or tracing
console.log("Hello, World!");

// Set element in HTML above using DOM (Document Object Model)
document.getElementById("output").textContent = "Hello, World!";

// Jupyter built in magic element for testing and convenience of development
element.textContent = "Hello, World!";  // element is an output option as part of %%js magic

//alert("Hello, World!");

<IPython.core.display.Javascript object>

multiple outputs using one variable

This second example is a new sequence of code, two or more lines of code forms a sequence. This example defines a variable, thank goodness!!! In the previous example we were typing the string "Hello, World" over and over. Observe with the variable msg="Hello, World!"; we type the string once and now use msg over and over.

%%js
console.log("Variable Definition");

var msg = "Hello, World Again!";

// Use msg to output code to Console and Jupyter Notebook
console.log(msg);  //right click browser select Inspect, then select Console to view
document.getElementById("output").textContent = msg;
element.append(msg);
//alert(msg);


<IPython.core.display.Javascript object>

output showing use of a function

This example passes the defined variable “msg” to the newly defined “function logIt(output)”.

%%js
console.log("Function Definition");

/* Function: logIt
 * Parameter: output
 * Description: The parameter is "output" to console and jupyter page
*/
function logIt(msg) {
    console.log(msg); 
    element.append(msg);
    document.getElementById("output").textContent = msg;
    //alert(output);
}

// sequence of code build logIt parameter using concatenation
var msg = "Hello, Students!" // replaces content of variable
var classOf = "Welcome CS class of 2023-2024."
logIt(msg + "  " + classOf); // concatenation of strings

<IPython.core.display.Javascript object>

output showing Loosely typed data

JavaScript is a loosely typed language, meaning you don’t have to specify what type of information will be stored in a variable in advance.

%%js
console.log("Examine Data Types");

// Function to add typeof to output
function getType(output) {
    return typeof output + ": " + output;
}

// Function defintion
function logIt(msg) {
    console.log(getType(msg));  // logs string
    console.info(msg);          // logs object
    document.getElementById("output").textContent = msg;
    element.append(getType(msg) + " ");  // adds to Jupyter output
    //alert(getType(msg));
}

// Common Types
element.append("Common Types ");
logIt("Mr M"); // String
logIt(1997);    // Number
logIt(true);    // Boolean

// Object Type, this definition is often called a array or list
element.append("Object Type, array ");
var scores = [
    90,
    80, 
    100
];  
logIt(scores);

// Complex Object, this definition is often called hash, map, hashmap, or dictionary
element.append("Object Type, hash or dictionary ");
var person = { // key:value pairs seperated by comma
    "name": "Mr M", 
    "role": "Teacher"
}; 
logIt(person);
logIt(JSON.stringify(person));  //method used to convert this object into readable format

<IPython.core.display.Javascript object>

Build a Person object, JSON, and show output

JavaScript and other languages have special properties and syntax to store and represent data. In fact, a class in JavaScript is a special function.

%%js
console.log("Person objects");

/* class: Person
 * Description: A collection of Person data
*/
class Person {
  /* method: constructor
   * parameters: name, ghID - GitHub ID, classOf - Graduation Class 
   * description: returns object when "new Person()" is called with matching parameters
   * assignment: this.name, this.ghID, ... are properties retained in the returned object
   * default: role uses a default property, it is set to "Student"
  */
  constructor(name, ghID, classOf, role="Student") {
    this.name = name;
    this.ghID = ghID;
    this.classOf = classOf;
    this.role = role;
  }

  /* method: setter
   * parameters: role - role in classroom
   * description: this.role is updated from default value to value contained in role parameter
  */
  setRole(role) {
    this.role = role;
  }
  
  /* method: getter
   * description: turns properties of object into JSON object
   * return value: JSON object
  */
  getJSON() {
    const obj = {type: typeof this, name: this.name, ghID: this.ghID, classOf: this.classOf, role: this.role};
    const json = JSON.stringify(obj);
    return json;
  }

  /* method: logIT
   * description: this Person object is logged to console
  */
  
  logIt() {
    //Person Object
    console.info(this);
       
    // HTML output
    document.getElementById("output").textContent = this.getJSON();

    //Log to Jupter
    element.append(this.role + " object in JSON: ");
    element.append(this.getJSON());  
    element.append(" ");


    //alert(this.getJSON());
  }
    
}

// make a new Person Object
const teacher = new Person("Mr M", "jm1021", 1977); // object type is easy to work with in JavaScript
// update role to Teacher
var role = "Teacher";
teacher.setRole(role); // set the role
teacher.logIt();  // log to console

// make a new Person Object
const student = new Person("Jane Doe", "jane", 2007); // object type is easy to work with in JavaScript
student.logIt(); // log to console

<IPython.core.display.Javascript object>

Build a Classroom Array/List of Persons, JSON, and show output

Many key elements are shown again. New elements include…

%%js
console.log("Classroom object");

/* class: Person
 * Description: A collection of Person data
*/
class Person {
  /* method: constructor
   * parameters: name, ghID - GitHub ID, classOf - Graduation Class 
   * description: returns object when "new Person()" is called with matching parameters
   * assignment: this.name, this.ghID, ... are properties retained in the returned object
   * default: this.role is a default property retained in object, it is set to "Student"
  */
  constructor(name, ghID, classOf, role="Student") {
    this.name = name;
    this.ghID = ghID;
    this.classOf = classOf;
    this.role = role;
  }

  /* method: setter
   * parameters: role - role in classroom
   * description: this.role is updated from default value to value contained in role parameter
  */
  setRole(role) {
    this.role = role;
  }
  
  /* method: getter
   * description: turns properties of object into JSON object
   * return value: JSON object
  */
  getJSON() {
    const obj = {type: typeof this, name: this.name, ghID: this.ghID, classOf: this.classOf, role: this.role};
    const json = JSON.stringify(obj);
    return json;
  }

  /* method: logIT
   * description: this Person object is logged to console
  */
  logIt() {
    //Person Object
    console.info(this);
    // HTML output tag
    document.getElementById("output").textContent = this.getJSON();

    //Log to Jupter
    element.append("Person json <br>");
    element.append(this.getJSON() + "<br>"); 

    //alert(this.getJSON());
  }
    
}

/* class: Classroom
 * Description: A collection of Person objects
*/
class Classroom {
  /* method: constructor
   * parameters: teacher - a Person object, students - an array of Person objects
   * description: returns object when "new Classroom()" is called containing properties and methods of a Classroom
   * assignment: this.classroom, this.teacher, ... are properties retained in the returned object
  */
  constructor(teacher, students) {
    /* spread: this.classroom contains Teacher object and all Student objects
     * map: this.json contains of map of all persons to JSON
    */
    this.teacher = teacher;
    this.students = students;
    this.classroom = [teacher, ...students]; // ... spread option
    this.json = '{"classroom":[' + this.classroom.map(person => person.getJSON()) + ']}';
  }

  /* method: logIT
   * description: this Classroom object is logged to console
  */
  logIt() {
    //Classroom object
    console.log(this);

    // HTML output
    document.getElementById("data").textContent = this.json;
    document.getElementById("output").textContent = this.json;

    //Classroom json
    element.append("Classroom object in JSON: ");
    element.append(this.json);

    //alert(this.json);
  }
}

/* function: constructCompSciClassroom
 * Description: Create data for Classroom and Person objects
 * Returns: A Classroom Object
*/
function constructCompSciClassroom() {
    // define a Teacher object
    const teacher = new Person("Mr M", "jm1021", 1977, "Teacher");  // optional 4th parameter

    // define a student Array of Person objects
    const students = [ 
        new Person("Anthony", "tonyhieu", 2022),
        new Person("Bria", "B-G101", 2023),
        new Person("Allie", "xiaoa0", 2023),
        new Person("Tigran", "Tigran7", 2023),
        new Person("Rebecca", "Rebecca-123", 2023),
        new Person("Vidhi", "VidhiKulkarni", 2024)
    ];

    // make a CompSci classroom from formerly defined teacher and student objects
    return new Classroom(teacher, students);  // returns object
}

// assigns compsci to the object returned by "constructCompSciClassroom()" function
const compsci = constructCompSciClassroom();
// output of Objects and JSON in CompSci classroom
compsci.logIt();


<IPython.core.display.Javascript object>

for loop to generate Table Rows in HTML output

This code extracts JSON text from HTML, that was placed in DOM in a previous JavaScript cell, then it parses text into a JavaScript object. In addition, there is a for loop that iterates over the extracted object generating formated rows and columns in an HTML table.

    ----------------
    |     HTML     |
    |     DOM      | 
    | data  output |  - ref: id="data", id="output"
    ----------------
       ⇓      ⇑
      get    set
    ----------------
    | JavaScript   | - get data: 
    |    code      |    const jsonText = document.getElementById("data").innerHTML;
    |getElementById| - set output: 
    ----------------    document.getElementById("output").innerHTML = htmlOut;


%%js
console.log("Classroom Web Page");

// extract JSON text from output element in HTML page
const jsonText = document.getElementById("data").innerHTML;

// convert JSON text to a JavaScript Object to process
const classroom = JSON.parse(jsonText).classroom;
console.log(classroom);

// make an HTML Out format for pretty display
/* Template literals (`), can make HTML generation more concise;
 * the map functions generates row strings and the join method combines them;
 * this replaces longer and ugly for loop and string concatenation.
*/
const htmlOut = `
    <table>
        <thead>
            <tr>
                <th>Name</th>
                <th>GitHub ID</th>
                <th>Class Of</th>
                <th>Role</th>
            </tr>
        </thead>
        <tbody>
            ${classroom.map(row => `
                <tr>
                    <td>${row.name}</td>
                    <td>${row.ghID}</td>
                    <td>${row.classOf}</td>
                    <td>${row.role}</td>
                </tr>
            `).join('')}
        </tbody>
    </table>
`;

// assign/set htmlOut to output element in HTML page
document.getElementById("output").innerHTML = htmlOut;

// show raw HTML
console.log(htmlOut);
element.append(htmlOut);

<IPython.core.display.Javascript object>

Hacks

Work with output and objects.

  • Adapt this tutorial to your own work and interests, how many steps do you understand?
  • Relate console output on last step to a previous hack
  • Explain, how console.log can help find errors in code?
  • Try out ChatGPT Jupyter features; though I prefer using Web and cut-copy-paste