JS Output w/ Objects
Quick launch into Variables, Functions, Arrays, Classes, Objects.
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.
- JavaScript / Jupyter General References
- W3Schools HTML Reference
- W3Schools JS Reference
- Theme setup for Jupyter Article. Or do these commands from shell…
- Install pip: pip install jupyterthemes
- Revert to original theme: jt -r
- List themes: jt -l
- Install with Theme, Name, Logo: jt -t onedork -T -N -kl
Output using HTML and CSS
Multiple cells are used to setup HTML in this lesson. Many of the JavaScript cells will use the data and output tag(s) to write into the HTML DOM that has been setup.
Output to HTML is the way to interact with the user.
This is a “classic” html definition.
- %%html: This magic command is used in Jupyter Notebooks to write and run HTML code directly within a cell.
- style tag is used to define CSS styles for the HTML elements, allowing you to customize the appearance.
- p tag with id attribute uniquely identifies the element, making it easy to access and manipulate data with JavaScript.
- div tag with class attribute is a container for other HTML elements. The class attribute allows you to apply CSS styles to HTML elements within the div container.
%%html
<!-- html enabled cell -->
<html>
<head>
<style>
.white-on-dark {
color: #00a526; /* short-hand for #ffffff, which is white */
background-color: #722b7a; /* color code for dark grey */
padding: 10px; /* padding around text */
border: 7px solid #1ac5b1; /* short-hand for #cccccc, which is light grey */
}
</style>
</head>
<body>
<!-- Hide raw data in page -->
<p id="data" hidden>
Initial secret data 2
</p>
<!-- Output HTML data within container -->
<div class="white-on-dark" id="output">
Hello!
</div>
</body>
</html>
Initial secret data 2
Hello!
Color Code
They are represented in Hexadecimal which is a shorthand for binary.
Break down
Here is a brief.
| Intensity | Red Binary Digits | Red Hex | Blue Hex | Green Hex |
|---|---|---|---|---|
| No Red | 0000 0000 | #00 | #00 | #00 |
| Weak Red | 0000 1111 | #0F | #00 | #00 |
| Strong Red | 1111 0000 | #F0 | #00 | #00 |
| Max Red | 1111 1111 | #FF | #00 | #00 |
Alter Color Combination
Pick your own color and background-color in the HTML.
Hidden Data
Data can be on the page, but not visible. This is a common technique in HTML/JavaScript programming.
Alter the Hidden Data to your own message.
%%js
// Extrat the hidden data from the page
var dataElement = document.getElementById('data');
if (dataElement) {
// Display the data in the console
console.log(dataElement.innerText);
} else {
console.error('Element with id "data" not found.');
}
<IPython.core.display.Javascript object>
Other outputs explored
There are several ways to ouput the classic introduction message: “Hello, World!”
These “other outputs” are for developers.
- Before you go further, open Console on your Browser. JavaScript developer leaves Console open all the time!!!
- The function console.log() outputs to Console, this is often used for inspection or debugging.
- “Hello, World” is a String literal. This is the referred to as Static text, as it does not change. Developer call this a hard coded string.
- "Hello, World" literal is a parameter to console.log(), element.txt() and alert().
- The element.textContent is part of Jupyter Notebook %%js magic. This is convenient for Notebook and testing.
- The alert command outputs the parameter to a dialog box, so you can see it in this Jupyter notebook. The alert commands are shown, but are commented out as the stop run all execution of the notebook.
- Note, in a Web Application Debugging: An alert is often used for less savy Developers. Console is used by more savy developers; console often requires setting up a lot of outputs. Source level debugging is the most powerful solution for debugging and does not require alert or console commands.
%%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!");
// HTML page output using DOM (Document Object Model) from previous cell
document.getElementById("output").textContent = "Hello, World!";
// Jupyter Only, output for development
element.append("Hello, World!"); // element is an output option as part of %%js magic
// alert("Hello, World!");
<IPython.core.display.Javascript object>
multiple outputs using a 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.
- The variable “var msg =” is used to capture the data
- The console.log(msg) outputs to console, be sure to Inspect it!
- The element.text() is part of Jupyter Notebooks and displays as output blow the code on this page. Until we build up some more interesting data for Web Site, we will not use be using the Python HTML, CSS technique.
- The alert(msg) works the same as previous, but as the other commands uses msg as parameter.
%%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)”.
- There are multiple steps in this code..
- The definition of the function: “function logIt(output) {}” and everything between curly braces is the definitions of the function. Passing a parameter is required when you call this function.
- The “call to the function:”logIt(msg)” is the call to the function, this actually runs the function. The variable “msg” is used a parameter when calling the logIt function.
- Showing reuse of function…
- There are two calls to the logIt function
- This is called Prodedural Abstraction, a term that means reusing the same code
%%js
console.log("Function Definition");
/* Function: logIt
* Parameter: msg
* Description: The parameter is "msg" is output to console, jupyter and "output" element in HTML
*/
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 2024-2025."
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.
- To define a variable you prefix the name with var or const. The variable type is determined by JavaScript at runtime.
- Python and many interpretive languages are loosely typed like JavaScript. This is considered programmer friendly.
- Java which is a compiled language is strongly typed, thus you will see terms like String, Integer, Double, and Object in the source code.
- In JavaScript, the typeof keyword returns the type of the variable. Become familiar with type as it is valuable in conversation and knowing type help you understand how to modify data. Each variable type will have built in methods to manage content within the data type.
%%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.
- Definition of class allows for a collection of data, the “class Person” allows programmer to retain name, github id, and class of a Person.
- Instance of a class, the “const teacher = new Person(“Mr M”, “jm1021”, 1977)” makes an object “teacher” which is an object representation of “class Person”.
- Setting and Getting properties After creating teacher and student objects, observe that properties can be changed/muted or extracted/accessed.
%%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 = {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…
- Building an Array, “const students” is an array of many students.
- Building a Classroom, this shows combining using spread.
%%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 = {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.
- Table generation is broken into parts…
- table data is obtained from a classroom array inside of the extracted object.
- the JavaScript for loop allows the construction of a new row of data for each Person hash object inside of the the Array.
- in the loop a table row
<tr> ... </tr>is created for each Hash object in the Array. - in the loop table data, a table column,
<td> ... </td>is created for name, ghID, classOf, and role within the Hash object.
----------------
| 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;
console.log(jsonText);
// 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.
- Explain each of the outputs types.
- Using the last two code cells. Make a table of Cars, Games, Team Member. Something that you and pair share as interests.