Switch Statements

The final type of conditional statement is the switch statement.
Switch statements are used to “switch” among a number of conditions called cases, instead of including tons of else if statements.
The cases compare the value of the tested variable/value to the value attributed to the case.
Once the correct value is found, the code in that case is executed.
If no cases match the tested value, the switch statement executes the “default case”

Examples:

This first switch statement will test different conditions to see what today is, in terms of the name of the day.
The switch statement will do this by utilizing a JavaScript date object, which will be covered in a later segment.
The variables ‘today’ and ‘day’ get the current date from the JavaScript Date object. Objects are covered in a later segment.

On line 35, the value of the day is returned to us in a numeric format, with 0 representing Sunday, 1 representing Monday, and so on.
We use a switch statement instead of 7 if, else if, else statements to determine what day it is:
The variable day is compared to the values of each case. When the value is matched, the day is printed.

We always include a default statement in switch statements in case of an error on our part, or in case none of the cases evaluate as true.
The default case also helps with troubleshooting instead of not having any output when something goes wrong.

// today is a variable storing a new JavaScript Date object. 
let today = new Date;
// day is a variable storing the numeric value for today's day out of the week
let day = today.getDay();

// Pay attention to the syntax of the switch statement. First, begin with the keyword switch() with the tested variable within the parenthesis:
// The switch statement's cases go inside of the curly brackets:

switch (day) {
  // The first case on the next line contains the code to execute in the case that day is equal to 0. This is the equivalent of testing " if(day == 0) "
  case 0:
    // if this case is true, the day is Sunday. We print this to the console.
    console.log("It's Sunday");
    // It is important to include a break statement at the end of each case in a switch statement, so that the program stops checking each condition after the case has evaluated as true, and the switch statement is exited
    // Ensuring that the program does not continue to check the rest of the cases improves the program's efficiency 
    break;
    // the next line is the equivalent of testing " if(day == 1) "
  case 1:
    console.log("It's Monday");
    break;
  case 2:
    console.log("It's Tuesday");
    break;
  case 3:
    console.log("It's Wednesday");
    break;
  case 4:
    console.log("It's Thursday");
    break;
  case 5:
    console.log("It's Friday");
    break;
  case 6:
    console.log("It's Saturday");
    break;
    // the default case is simply declared by saying default: rather than case ___: 
  default:
    console.log("It's today");
}

We can also program switch statements that check more complex conditions
To do so, we set the variable the switch statement is checking to “true”.
Now, we can set the conditions for the cases to more complex conditions, such as the cases below:

This switch example determines the letter grade of a test score out of 100

let testScore = 73;

// Note that we use 'true' in place of the tested variable, and incorporate the testScore variable in the case conditions
switch (true) {
  case testScore >= 90:
    console.log(testScore + " / 100 : A");
    break;
  case testScore >= 80:
    console.log(testScore + " / 100 : B");
    break;
  case testScore >= 70:
    console.log(testScore + " / 100 : C");
    break;
  case testScore >= 60:
    console.log(testScore + " / 100 : D");
    break;
  case testScore >= 70:
    console.log(testScore + " / 100 : F");
    break;
  default:
    console.log("Score is too low to even have a grade");
}

Switch statements