Note: If you're new to TypeScript, check our Getting Started with TypeScript tutorial first.
The TypeScript switch...case statement executes different blocks of code based on the value of a given expression.
Here's a simple example of the switch...case statement. You can read the rest of the tutorial to learn more.
Example
let trafficLight: string = "green";
let message: string = ""
switch (trafficLight) {
case "red":
message = "Stop immediately.";
break;
case "yellow":
message = "Prepare to stop.";
break;
case "green":
message = "Proceed or continue driving.";
break;
default:
message = "Invalid traffic light color.";
}
console.log(message)
// Output: Proceed or continue driving.
The above program checks the value of trafficLight and prints its corresponding meaning. If the value doesn't match any of the specified cases, it prints Invalid traffic light color.
Syntax of the switch...case Statement
switch (expression) {
case value1:
// Code block to be executed
// if expression matches value1
break;
case value2:
// Code block to be executed
// if expression matches value2
break;
...
default:
// Code block to be executed
// if expression doesn't match any case
}
Here,
- The
switchstatement first evaluates theexpression. - After that, it compares the result against value1. If a match is found, the corresponding code block is executed. Then, the
breakstatement immediately stops further checking of other cases. - If there's no match for value1, the program compares the result with the next specified case value (value2). This process continues until a matching case is found.
- If none of the case values match, the code block in the
defaultblock is executed.
Let's try to understand this process with the flowchart below.
Flowchart of switch Statement
Example 1: Simple Program Using switch...case
Suppose we want to display a message based on the current day of the week. Let's look at the example below to see how we can achieve this using switch...case.
let day: number = 3;
switch (day) {
case 1:
console.log("Sunday");
break;
case 2:
console.log("Monday");
break;
case 3:
console.log("Tuesday");
break;
case 4:
console.log("Wednesday");
break;
case 5:
console.log("Thursday");
break;
case 6:
console.log("Friday");
break;
case 7:
console.log("Saturday");
break;
default:
console.log("Invalid Day");
}
Output
Tuesday
This program prints the day based on the number stored in the day variable (1 for Sunday, 2 for Monday, and so on).
Here, the switch statement checks the value of day against a series of cases:
- First, it checks day against
case 1. Since it doesn't match, this case is skipped. - Next, it checks day against
case 2. Since it doesn't match, this case is skipped. - Then, it checks day against
case 3. Since there's a match, its code block is executed (Tuesdayis printed). - After printing
Tuesday, abreakstatement is encountered, which terminates theswitchstatement.
Note: Because of TypeScript's strict type checking, you can't check variables/expressions of one type with case values of other types. For example,
let day: number = 3;
switch (day) {
// Error due to comparison between number variable and string literal
case "1":
console.log("Sunday");
break;
... ... ...
}
Example 2: Simple Calculator Using switch...case
// Take user input for first number
let userInput: string | null = prompt("Enter the value of number1: ");
const number1: number = Number(userInput);
// Take user input for second number
userInput = prompt("Enter the value of number2: ");
const number2 = Number(userInput);
// Take user input to select an operator
const operator: string | null = prompt("Enter an operator ( either +, -, * or / ): ");
// Variable to store the result of calculation
let result: number;
switch(operator) {
case "+":
result = number1 + number2;
console.log(`${number1} + ${number2} = ${result}`);
break;
case "-":
result = number1 - number2;
console.log(`${number1} - ${number2} = ${result}`);
break;
case "*":
result = number1 * number2;
console.log(`${number1} * ${number2} = ${result}`);
break;
case "/":
result = number1 / number2;
console.log(`${number1} / ${number2} = ${result}`);
break;
default:
console.log("Invalid operator");
}
Sample Output 1
Enter the value of number1: 6 Enter the value of number2: 3 Enter an operator ( either +, -, * or / ): * 6 * 3 = 18
Sample Output 2
Enter the value of number1: 6 Enter the value of number2: 3 Enter an operator ( either +, -, * or / ): + 6 + 3 = 9
In the above program, we prompted the user to:
- Enter two numbers: number1 and number2.
- Select an operator:
+,-,*, or/.
Based on the user input, the switch statement performs the corresponding calculation.
Note: Here, we have used template literal `${number1} + ${number2} = ${result}` that combines text and variable into one string.
It shows the values of number1, number2, and result directly in the message, like 5 + 3 = 8. To learn more about template literals, visit TypeScript Template Literals.
More on TypeScript switch Statement
It is not necessary to use the default case in TypeScript. For example,
let country: string = "Nepal";
switch (country) {
case "USA":
console.log("American");
break;
case "UK":
console.log("British");
break;
case "Japan":
console.log("Japanese");
}
console.log("Code after switch statement")
// Output: Code after switch statement
We haven't used a default case in the program above. Moreover, the value of the country variable doesn't match any of the cases in the switch statement.
In such cases, the switch statement is skipped entirely and the program flow goes to the line that comes after the body of the switch statement.
So far, we have used a break statement inside each case block. For example,
case 2:
console.log("Monday");
break;
The break statement terminates the execution of the switch statement once a matching case has been found.
Without break, the program would continue executing subsequent cases even after finding a match. For example,
let fruit: string = "banana";
switch (fruit) {
case "apple":
console.log("Apple case");
case "banana":
console.log("Banana case");
case "orange":
console.log("Orange case");
default:
console.log("Unknown fruit");
}
Output
Banana case Orange case Unknown fruit
Sometimes, we may want multiple case values to trigger the same block of code. For this, we can use multiple cases with a single block.
Let's look at an example to understand this clearly.
// Program to categorize age
let age: number = 19;
switch (age) {
// When age is 13, 14, or 15
case 13:
case 14:
case 15:
console.log("Early Teen")
break;
// When age is 16 or 17
case 16:
case 17:
console.log("Mid Teen");
break;
// When age is 18 or 19
case 18:
case 19:
console.log("Late Teen");
break;
// When age is none of the above
default:
console.log("Other Age Group");
}
Output
Late Teen
In this program, we have grouped multiple cases together, which allows us to use a single block of code for all the cases in the group. These groups are:
- cases 13, 14, and 15 - Prints
Early Teento the screen. - cases 16 and 17 - Prints
Mid Teento the screen. - cases 18 and 19 - Prints
Late Teento the screen.
Since 19 matches the second case in the third group (case 19), Late Teen is printed as an output.
Both switch...case and if...else statements are used for decision-making. However, they are useful in different conditions:
switch- Use it to check for a large number of conditions based on the same expression, which can be more readable thanif...else.if...else- Use it for complex logical conditions that can't be easily expressed as discrete cases.
Let's look at two programs that perform the same task, one by using a switch statement and another by using if...else:
// Program using switch statement
let color: string = "green";
switch (color) {
case "red":
console.log("Stop");
break;
case "yellow":
console.log("Caution");
break;
case "green":
console.log("Go");
break;
default:
console.log("Invalid color");
}
// Output: Go
In the above program, the color variable is compared against each case. When it matches the case "green", Go is printed as output.
// Program using if...else statement
let color: string = "green";
if (color === "red") {
console.log("Stop");
}
else if (color === "yellow") {
console.log("Caution");
}
else if (color === "green") {
console.log("Go");
}
else {
console.log("Invalid color");
}
// Output: Go
Here, the if...else statement checks the value of color against various conditions.
When color matches "green", the corresponding block executes, printing Go as the output.
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