W1D1 - Welcome!

- Welcome Lecture
- Morning Lecture
- Solo Work!

How To Learn

• Passive
  • Readings, Flashcards, Videos, Discussions
• Active
  • Coding, Quizzes, Assessments
• Desirable Difficulty
  • You should feel challenged throughout the course
  • At the same time, we aren’t asking you to build a full app this week
  • Difficulty and complexity will increase throughout the course
• Repetition:
  • You’ll notice repeating information throughout the course. This is intentoinal!

The Number Type

• NOTE: console.log is a function in javascript which ‘prints’ or ‘logs’ the return value of the inputted code to your console.

    console.log(1 + 1);   // 2
    console.log(2.5 - 2); // 0.5
    console.log(3 * 4);   // 12 
    console.log(10 / 2);  // 5

    // Modulo (%) calculates remainder 
    console.log(25 % 5); //5r0 -> 0
    console.log(26 % 5); //5r1 -> 1
    console.log(27 % 5); //4r2 -> 2

String Type

• Single quotes or Double quotes
  • Be consistent
    • ‘hello’
    • “hello”
    • "hello’ -> BAD!
• Length
  • The .length method returns the number of characters in a string:
    • 'code'.length -> 4
• Indexing Strings
  • Think of an “Index” as the positioning of elements
  • Indices start at 0

    // length
    console.log('code'.length);

    // using brackets
    console.log('code'[0]); // 'c'
    console.log('code'[1]); // 'o'
    console.log('code'[2]); // 'd' 

    // indexOf
    console.log('code'.indexOf('c')); // 0
    console.log('cool code'.indexOf('o')); // 1
    console.log('cool code'.indexOf('a')); // return undefined

Boolean

• What is it?
  • true or false
• Not Operator (!)
  • Flips the value of a boolean
  • !true -> false instead of true
• The “And” Operator
  • Only true if both sides are true
  • true && false -> false

• The “Or” Operator (||)
  • True if either side is true
  • true || false -> true

Comparison

    // Less than/Greater than
    console.log(5 < 9);      // true
    console.log(5 > 9);      // false
    console.log('a' < 'b');  // true (dictionary order)
    console.log('cat' < 'cats'); // true (dictionary order)

    // Inclusive comparison
    console.log(7 <= 10);    // true
    console.log(10 >= 10);   // true 

    // Equality === and !==
    console.log(2 === 2);    // true
    console.log(2 === 2.1);  // false
    console.log(2 !== 2.1);  // true

    // Two equality operators, === and ==
    console.log(5 === '5'); // false
    console.log(5 == '5');  // true (types are coerced)
    console.log([] == 0);   // true (can be unpredictable)

Variables

    // initialization:
    //   - declaration, creating the space for the variable
    //   - assignment, giving a value to the variable

    let state;  // declaration using javascript 'let'
    console.log(state);
    state = 'California'; // assignment
    console.log(state);

    let city = 'Sacramento'; // both (i.e. initialized in one line)
    console.log(city);

    // more assignment
    let age = 5;
    console.log(age); // 5
    age + 5;          // no assignment used, i.e. change not permanent
    console.log(age); // 5
    age = age + 5;    // assignment is used, change is permanent
    console.log(age); // 10
    age += 5;         // assignment is used, this is shorthand
    console.log(age); // 15

    // Using ++ and -- 
    age++;
    console.log(age); // 16
    age--;
    console.log(age); // 15

Functions

• blocks of code that we can invoke multiple times
• prevent us from having to rewrite code

How to define your own function:

// keyword    name        parameters        code block
function nameOfFunction(parameter1, parameter2){
  // code to run whenever we invoke/call the function
}

How to call a function:

• Using parentheses invokes the function.

  nameOfFunction(argument1, argument2);

return keyword

• By default, functions will return undefined.

• If we want to return anything else, we use the return keyword:

  function addTwo(num1, num2) {
    return num1 + num2;
  }
  console.log(addtwo(1, 2)); // 3

• The return keyword stops executing code, nothing else below is run

  function addTwo(num1, num2) {
      console.log("I will be run.");
      return num1 + num2;
      console.log("I won't be run."); /// after the return, will not be run
    }
  console.log(addTwo(1, 2)); 
  // "I will be run."
  // 3