console.log output

Output to console using the classic programming introduction using a "Hello, World!" message.

  • The command or function is console.log()
  • "Hello, World" is a String literal. This is the referred to as Static text, as it does not change.
  • "Hello, World" is a parameter to the console.log command.
  • The console.log command outputs the parameter to the console, so you can see it in this Jupyter document.
  • Note, in a Web Application, console.log is used for debugging and is not visible from the browser via HTML. It is used behind the scenes, when using Inspect->Console from the browser.
console.log("Good afternoon, World!"); 
//python equivalent = print("insert text here")
// console log helps us debug our pages
Good afternoon, World!

console.log output showing use of variable

This second example is a sequence of code, two or more lines forms a sequence. This example defines a variable, then outputs the msg to terminal.

  • The variable "var msg =" is used to capture the data
  • The console.log(msg) outputs to console
//python equivalent: msg = "Goodnight, World!";
var msg = "kachow"; //remember to put semicolons!
console.log(msg);
kachow

console.log output showing use of a function

This example passes the previously defined variable "msg" to the newly defined "function logIt(output)".

  • There are two steps in the code, the definition of the function and the call to the function.
    • "function logIt(output) {}" and everything between curly braces is the definitions of the function.
    • "logIt(msg)" is the call to the function, this actually activates the function. If you remove this line you will not receive any output to console.
  • Since the variable "msg" was defined in previous cell, it is used a parameter when calling the logMessage function.
function logIt(output) {
    console.log(output);
}
logIt(msg); //message becomes the output of the function
//in jupyter notebooks, you don't need to re-define the variable, because we ran the cells above that already have the variable "msg" defined
kachow

Showing reuse of a function

Now that a function is defined, it can be called from any of the subsequent cell in the Jupyter notebook. A function/method, is a process of creating a procedural abstraction. This a programming practice to promote reuse versus coding the same thing over and over.

  • First call sends a different string message
  • Second call sends a number
console.log("Reuse of logIT") 
logIt("Hello, Students!"); //defining logIt
logIt(2022)
Reuse of logIT
Hello, Students!
2022

Dynamic or Loosely typed language (string, number)

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. The variable type is determined at runtime. This is similar to Python and most interpretive languages. Java which is a compiled language is strongly typed, thus you will see string, integer, double, and object in the source code. In JavaScript, the "typeof" keyword returns the type.

function logItType(output) {
    console.log(typeof output, ";", output);
}
console.log("Looking at dynamic nature of output types in JavaScript") //calling all the logIt types
logItType("hello"); // String
logItType(2020);    // Number
logItType([1, 2, 3]);  // List -- called an "object" in the output -- Object is generic for this Array, which similar to Python List
// there are different names for the types of print outputs, like string, number, and object
Looking at dynamic nature of output types in JavaScript
string ; hello
number ; 2020
object ; [ 1, 2, 3 ]

Build a Person Function/Class object and JSON

JavaScript functions have special properties and syntax is shown in many ways. In fact, a Class in JavaScript is a special function. Jupyter Notebooks seems to be more friendly to "function" definitions versus "Class", thus this lesson uses "function" and "prototype" versus "Class".

  • Definition of function allows for a collection of data, the "function Person" allows programmer to retain name, github id, and class of designation.
  • Definition of a prototype allow for the definition of a method associated with the function , the "Person.prototype.toJSON" allows the collection of data to be expressed in a json/string versus JavaScript object.
  • Instance of a function, the "var teacher = new Person("Mr M", "jm1021", 1977)" line makes a variable "teacher" which is an object representation of "function Person".
// define a function to hold data for a Person
// critical part of every programming language is data
function Person(name, ghID, classOf) {
    this.name = name;
    this.ghID = ghID;
    this.classOf = classOf;
    this.role = "";
}

// define a setter for role in Person data
Person.prototype.setRole = function(role) {
    this.role = role;
}

// define a JSON conversion "method" associated with Person
// starting a function called .toJSON
// JSON is a way for us to share data
Person.prototype.toJSON = function() {
    const obj = {name: this.name, ghID: this.ghID, classOf: this.classOf, role: this.role};
    const json = JSON.stringify(obj);
    return json;
}

// make a new Person and assign to variable teacher
var teacher = new Person("Mrs. Derksen", "none", 1990);
teacher.setRole("Teacher");

// output of converting the Object and JSON/string associated with Teacher
logItType(teacher);  // object type is easy to work with in JavaScript
logItType(teacher.toJSON());  // json/string is useful when passing data on internet; data shows up as text on the internet
object ; Person {
  name: 'Mrs. Derksen',
  ghID: 'none',
  classOf: 1990,
  role: 'Teacher' }
string ; {"name":"Mrs. Derksen","ghID":"none","classOf":1990,"role":"Teacher"}

Build a Classroom Array/List of Persons and JSON

Many key elements are shown again. New elements include...

  • Building an Array, "var students" is an array of many persons
  • Building a Classroom, this show forEach iteration through an array and .push adding to an array. These are key concepts in all programming languages.
// define a student Array of Person(s)
var students = [ 
    new Person("Shreya", "rey444", 2023),
    new Person("Jiya", "jiya-sav", 2023),
    new Person("Sanika", "sanikasha", 2023),
    new Person("Noor", "Nope1013", 2023),
    new Person("Vaishavi", "vaishavi-chan", 2023),
    new Person("Rahul", "protein-shake", 2023),
    new Person("Sohni", "ok i pull up", 2023)
];

// define a classroom and build Classroom objects and json
function Classroom(teacher, students){ // 1 teacher, many student
    // start Classroom with Teacher
    teacher.setRole("Teacher");
    this.teacher = teacher;
    this.classroom = [teacher];
    // add each Student to Classroom
    this.students = students;
    this.students.forEach(student => { student.setRole("Student"); this.classroom.push(student); });
    // build json/string format of Classroom
    this.json = [];
    this.classroom.forEach(person => this.json.push(person.toJSON()));
}

// make a CompSci classroom from formerly defined teacher and students
compsci = new Classroom(teacher, students);

// output of Objects and JSON in CompSci classroom
logItType(compsci.classroom);  // constructed classroom object
logItType(compsci.classroom[0].name);  // abstract 1st objects name
logItType(compsci.json[0]);  // show json conversion of 1st object to string
logItType(JSON.parse(compsci.json[0]));  // show JSON.parse inverse of JSON.stringify
object ; [ Person {
    name: 'Mrs. Derksen',
    ghID: 'none',
    classOf: 1990,
    role: 'Teacher' },
  Person { name: 'Shreya', ghID: 'rey444', classOf: 2023, role: 'Student' },
  Person { name: 'Jiya', ghID: 'jiya-sav', classOf: 2023, role: 'Student' },
  Person {
    name: 'Sanika',
    ghID: 'sanikasha',
    classOf: 2023,
    role: 'Student' },
  Person { name: 'Noor', ghID: 'Nope1013', classOf: 2023, role: 'Student' },
  Person {
    name: 'Vaishavi',
    ghID: 'vaishavi-chan',
    classOf: 2023,
    role: 'Student' },
  Person {
    name: 'Rahul',
    ghID: 'protein-shake',
    classOf: 2023,
    role: 'Student' },
  Person {
    name: 'Sohni',
    ghID: 'ok i pull up',
    classOf: 2023,
    role: 'Student' } ]
string ; Mrs. Derksen
string ; {"name":"Mrs. Derksen","ghID":"none","classOf":1990,"role":"Teacher"}
object ; { name: 'Mrs. Derksen',
  ghID: 'none',
  classOf: 1990,
  role: 'Teacher' }

IJavaScript and Table formatting using toHTML method

This example builds a Classroom method _toHTML which is passed to the IJavaScript interpreter $$.html which renders output similarly to a real website.

  • JavaScript in the _toHTML method is broken into three parts...
    • Style part is building CSS inline formatting
    • Body part is constructing the Table Rows (tr), Table Headings (th), and Table Data (td). The table data is obtained from a Classroom object. The JavaScript for loop allows the construction of a new row of data for each person object in the Array.
    • Return part creates the HTML fragment for rendering
  • The last line in the example $$.html is IJavaScript HTML interpreter and by passing the parameter of the _toHTML method it obtains HTML to render
// define an HTML conversion "method" associated with Classroom
// converting the javascript data to HTML for organization is at end, using "$$.html is IJavaScript HTML interpreter"

Classroom.prototype._toHtml = function() {
  // HTML Style is build using inline structure
  // defining variable "style"
  var style = (
    "display:inline-block;" +
    "background:MediumPurple;" + // to change the color, search up "HTML color codes" and type the name of the color you want
    "border: 8px black;" +
    "fontcolor: black" +
    "box-shadow: 0.5em 0.5em 0.4em grey;"
  );

  // HTML Body of Table is build as a series of concatenations (+=)
  // concatenations = adding/building stuff
  var body = ""; // using "" to define the variable allows us to have multiple outputs for the variable
  // Heading for Array Columns
  body += "<tr>"; // tr = table rows
  body += "<th><mark style='color: black; background-color:pink'>" + "Name" + "</mark></th>"; // th = table headings
  body += "<th><mark style='color: black; background-color:pink'>" + "GitHub ID" + "</mark></th>";
  body += "<th><mark style='color: black; background-color:pink'>" + "Class Of" + "</mark></th>";
  body += "<th><mark style='color: black; background-color:pink'>" + "Role" + "</mark></th>";
  body += "</tr>";
  // Data of Array, iterate through each row of compsci.classroom 
  for (var row of compsci.classroom) {
    // tr for each row, a new line
    body += "<tr>";
    // td for each column of data
    body += "<td>" + row.name + "</td>"; // td = table data
    body += "<td>" + row.ghID + "</td>";
    body += "<td>" + row.classOf + "</td>";
    body += "<td>" + row.role + "</td>";
    // tr to end line
    body += "<tr>";
  }

   // Build and HTML fragment of div, table, table body
  return (
    "<div style='" + style + "'>" +
      "<table>" +
        body +
      "</table>" +
    "</div>"
  );

};

// IJavaScript HTML processor receive parameter of defined HTML fragment
$$.html(compsci._toHtml());
</table></div> </div> </div> </div> </div> </div> </div>
Name GitHub ID Class Of Role
Mrs. Derksen none 1990 Teacher
Shreya rey444 2023 Student
Jiya jiya-sav 2023 Student
Sanika sanikasha 2023 Student
Noor Nope1013 2023 Student
Vaishavi vaishavi-chan 2023 Student
Rahul protein-shake 2023 Student
Sohni ok i pull up 2023 Student