reading-notes

Class 7: Programming w/JavaScript

Resources

Some Notes

Control Flow

Control Flow = the order in which the cpu executes statements in a script.
- Code is run in order from first line to last line unless there are structures that change control flow, such as conditionals and loops.
A typical script in JS or PHP includes many control structures, including conditionals, loops and functions. Parts of a script may also be set to execute when events occur.

JavaScript Functions

A JS function is a block of code designed to perform a particular task.
Functions are executed when something “calls it”
- // Function to compute the product of p1 and p2 function myFunction(p1, p2) { return p1 * p2; }
For a procedure to qualify as a funtion, it should take some input and return an output where there is some obvious relationship between the input and output.

JavaScript Function Syntax

JS functions are defined with the function keyword, followed by a name, followed by parentheses ().
Function names follow same rules as variables (contains letters, digits, underscores, and dollar signs).
The code to be executed by the function is placed inside curly brackets {}.
function name(parameter1, parameter2, parameter3) { // code to be executed }

Function Return

When JS reaches a return statement, the function will stop executing.
If the function was called from a statement, JS will return to execute the code after the invoking statement.
Functions often compute a return value. The return value is “returned” back to the “caller”.
let x = myFunction(4, 3); // Function is called, return value will end up in x

function myFunction(a, b) { return a * b; // Function returns the product of a and b }

With functions you can define the code once and use it many times.
- You can use the same code many times with different arguments to produce different results.
  - function toCelsius(fahrenheit) { return (5/9) * (fahrenheit-32); } document.getElementById(“demo”).innerHTML = toCelsius(77);
The () Operator invokes the function
- function toCelsius(fahrenheit) { return (5/9) * (fahrenheit-32); } document.getElementById(“demo”).innerHTML = toCelsius;
Functions can be use as Variable values
- let x = toCelsius(77); let text = “The temperature is “ + x + “ Celsius”;

Local Variables

Variables declared within a JS function become LOCAL to the function.
- Local variables can only be accessed from within the function.
- // code here can NOT use carName

function myFunction() { let carName = “Volvo”; // code here CAN use carName }

// code here can NOT use carName

JavaScript Operators

The assignment operator (=) assigns a value to a variable.
- let x = 10;
The addition operator (+) adds numbers.
- let x = 5; let y = 2; let z = x + y;
The multiplication operator (*) multiplies numbers.
- let x = 5; let y = 2; let z = x * y;

Types of JS Operators

1. Arithmetic Operators
  - Additon = +
  - Subtraction = -
  - Multiplication = *
  - Exponentiation = **
  - Division = /
  - Modulus (Division Reminder) = %
  - Increment = ++
  - Decrement = –
1. Assignment Operators
  - += example (x += y)=(x= x + y)
  - -= example (x -= y)=(x= x - y)
  - *= example (x *= y)=(x= x * y)
  - /* example (x /= y)=(x= x / y)
  - %= example (x %= y)=(x= x % y)
  - **= example (x **= y)=(x= x ** y)
1. Comparison Operators
  - == eqaul to
  - === equal value and equal type
  - != not equal
  - !== not equal value or not equal type
  - greater than
  - < less than
  - = greater than or equal to
  - <= less than or equal to
  - ? ternary operator
1. Logical Operators
  - && logical and
  - logical or
  - ! logical not
1. Conditional Operators
1. Type Operators
  - typeof Returns the type of a variable
  - instanceof Returns true if an object is an instance of an object type

Replit Practice

// declaring a variable called theName // assigning it the value of the result of prompting // “What is your name?”

let favColor = “yellow” let userGuess = prompt(“What is my fav color?”); userGuess = userGuess.toLowerCase(); console.log(“Now user guess is: “ + userGuess); // console.log(“User guess is: “ + userGuess); if (userGuess == favColor){ console.log(“You are right.”); } else { console.log(“You are wrong.”); } // let userName = prompt(“What is your name?”);

if (userName == “ryan”) { console.log(“Hola compa, hear any good chisme on the cartel lately?”); } else { console.log(“Buenos Dias, Bolivia”) } console.log(“Welcome to Bolivia “ + userName); //

Things I Would Like to Know More About

Maybe in time, I will be able to memorize most of these operators, but as of right now there are soooooo many. I will have to reference the MDN often until I get the hang of these things.