CS.2510_Spring.2026_Topics/JS.html at main · CS2510/CS.2510_Spring.2026_Topics · GitHub

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<!doctype html>
<html>

<head>
  <title>JS From Python</title>
</head>

<body>
  <script>

    //
    // Comments
    //
    // Comments in JS can be either inline or block
    // Comments that start with two //s are inline -- they comment the remainder of the line of text
    // Coming from python, `//` is very similar to `#`
    // Comments that start with /* and end with */ are block -- they only comment what is between the beginning and ending of the /* and */
    // This is (somewhat) similar to docstrings

    // This is an inline comment

    /* This is a block comment */

    /*
    This is a multi-line block comment
    */

    //
    // Printing to the console
    //
    //You print to the console with `console.log`
    //Most browsers let you open the console with F12 or Ctrl+Shift+I

    console.log("This should be printed to the console.")
    console.log("") // Empty line in the console

    // Coming from python, `console.log()` is very similar to `print()`

    //
    // Variables
    //
    // In modern JS, variables start with `let` or `const`.
    // `let` means that the variable can change.
    // `const` means the variable cannot change.

    let a = 1
    const b = 2

    // Coming from python, `let a = 1` is similar to `a = 1`

    a = 2 // This is allowed since a was declared with `let`
    //b = 3 //This will throw an error in the console since b was declared as const

    // Variables - Warnings
    //
    // You can declare a variable using `var` or no keyword at all
    // This is old syntax and should be avoided, but you may see it used
    // in examples online.
    //
    // This syntax should be avoided because these variable have strange scoping rules
    // cause unexpected side effects

    var c = 3 //Don't use this older syntax
    d = 4 //Don't use this older syntax

    //
    // Strings
    //
    // Strings in JS can be denoted with `s, 's, or "s
    let name = `Alice`
    name = 'Betty'
    name = "Carla"

    // `` create interpolated strings
    // This is similar to f strings in python
    // except that variables are offset with ${} instead of just {}
    console.log(`I have ${d} cats`) // Similar to Python's print(f"I have {d} cats")
    console.log("")

    //
    // Numbers
    //
    // Numbers in JS are similar to those in Python
    const PI = 3.141

    // To truncate a number to be a float you have several options, depending on how you want the conversion to happen
    console.log(`Math.trunc PI: ${Math.trunc(PI)}`)
    console.log(`Math.ceil PI: ${Math.ceil(PI)}`)
    console.log(`Math.floor PI: ${Math.floor(PI)}`)
    console.log(`Math.round PI: ${Math.round(PI)}`)

    console.log("")

    console.log(`Math.trunc -PI: ${Math.trunc(-PI)}`)
    console.log(`Math.ceil -PI: ${Math.ceil(-PI)}`)
    console.log(`Math.floor -PI: ${Math.floor(-PI)}`)
    console.log(`Math.round -PI: ${Math.round(-PI)}`)

    // JS has an short-hand increment operator
    e = 10
    e++ // Identical to e += 1
    console.log("")
    console.log(e)

    // JS does not have Python's floor division, so you need to use one of the above methods

    //
    // Booleans
    //
    // Booleans in JS are spelled lower-case, i.e. `true` and `false`
    const easy = false

    //
    // Arrays (lists)
    //
    // Lists in JS are called arrays

    const people = ["Bob", "Millie"]

    // You get the length of a list using the length property
    console.log("")
    console.log(people.length)

    // You add to an array with `.push`
    people.push('Carl') //This is similar to Pythons .append()
    console.log(people)

    // Strangely, JS lacks a straightforward array delete method
    // Instead, you need to toSpliced or filter
    const friends = people.toSpliced(2, 1) //Remove elements starting at index 2. Remove 1 element
    console.log(friends)
    console.log("")

    //
    // Indentation/bracketing
    //
    // JS uses {}s instead of : and significant white space
    // The general rule is that anywhere you would use a :, you instead use a pair of {}s
    for (const person of friends) {
      console.log(person)
    }
    console.log("")

    //
    // Conditionals
    //
    //These work similar to Python, but require ()s and {}s
    if (2 > 1) {
      console.log("Hi")
    }
    console.log("")

    // JS uses the `&&` operator to mean `and` and the `||` operator to mean `or`
    if(3 > 2 || 3 > 1){} // instead of `if 3 > 2 or 3 > 1:`


    //
    // Loops
    //
    // JS supports for and while loops
    // Unlike python, they require ()

    let count = 0
    while (count < 5) {
      count++  // or count += 1
      console.log(count)
    }
    console.log("")

    // JS doesn't have a range() function, but you can use the three spots in a for loop to accomplish that
    for (let count = 0; count < 5; count++) {
      console.log(count)
    }
    console.log("")

    // JS has extended for loops as seen above with our loop over friends
    // !! Note that the syntax uses the `of` keyword, not `in`
    // `in` works, but loops over keys, not values. Don't worry about the technicality if you don't want to, just remember to use `of`
    for (const person in friends) { //This probably won't do what you expect
      console.log(person)
    }
    console.log("")

    //
    // Classes
    //
    // JS supports classes, but the syntax is a little different than in Python

    class Animal{

    }// Same as class Animal:

    class Dog extends Animal{

    }// Same as class Dog(Animal):

    // constructors in JS use the constructor keyword
    // In JS, you use `super()` instead of `super().__init__()`
    class Cat extends Animal{
      constructor(){
        super()
        console.log("Meow")
      }
    }

    //In JS, you instantiate an instance of a class with the `new` keyword

    const fido = new Cat() // Similar to Python's `fido = Cat()`

    // In JS, you access variables local to the instance with the `this` keyword
    class Frog extends Animal{
      constructor(){
        super()
        console.log("I am a frog")
        this.isAmphibian = true // As opposed to self.is_amphibian = True
      }
    }

    // In JS, static fields and functions are denoted with the 'static' keyword instead of the @staticmethod
    class Tesla{
      static inventor = "Musk" // Same for all calls to Tesla.inventor
      model //Varies for each instance of a Tesla

      static printInventor(){ //similar to @staticmethod
        console.log(inventor)
      }
    }


    //
    // Getters and setters
    //
    // In JS, you can control how variables are set and retrieved with getters and setters

    class PlayerHealth{

      _health = 50

      get health(){
        //Additional logic here
        return this._health
      }

      set health(value){
        this._health = value
        //Additional logic here
      }
    }


  </script>
</body>

</html>