The switch statement is used to move control to a specific inner case clause that specifies a value that matches the value passed to switch(...). It has the following syntax:

switch (SwitchExpression) SwitchBody

SwitchExpression will be evaluated once and its value compared via strict-equality to case statements within SwitchBody. Within SwitchBody there may be one or more case clauses and/or a default clause. The case clauses designate CaseExpression, whose value will be compared to that of SwitchExpression, and their syntax is as follows:

case CaseExpression:
  [other JavaScript statements or additional clauses]

The switch statement is usually used to specify a selection of two or more mutually exclusive outcomes based on a specific value. With fewer conditions, it'd be conventional to use an if...else construct, but to accommodate more potential conditions, it's simpler to use switch:

function generateWelcomeMessage(language) {

  let welcomeMessage;

  switch (language) {
    case 'DE':
      welcomeMessage = 'Willkommen!';
      break;
    case 'FR':
      welcomeMessage = 'Bienvenue!';
      break;
    default:
      welcomeMessage = 'Welcome!';
  }

  return welcomeMessage;
}

generateWelcomeMessage('DE'); // => "Willkommen!"
generateWelcomeMessage('FR'); // => "Bienvenue!"
generateWelcomeMessage('EN'); // => "Welcome!"
generateWelcomeMessage(null); // => "Welcome!"

Once the switch mechanism finds the appropriate case, it will execute all code following that case statement until the very end of the switch statement or until it encounters a break statement. A break statement is used to break out of SwitchBody when the desired work is accomplished.