Switch

Consider a variable in a Node.js program. We can test the variable's value in a switch statement—this may be a cleaner and faster way to perform the test.

When we use switch, we have a symmetrical construct that acts on possible values. This can make the code more elegant.

First example

It is good to start with a simple example. Here we see a switch statement inside a function called testValue. We pass an integer to testValue.

function testValue(value) {
    // Switch on the argument to return a number.
    switch (value) {
        case 0:
            return -1;
        case 1:
            return 100;
        case 2:
            return 200;
    }
    return 0;
}

// Call testValue.
console.log("SWITCH RESULT: " + testValue(0))
console.log("SWITCH RESULT: " + testValue(2))
SWITCH RESULT: -1
SWITCH RESULT: 200

Default

A case matches just one value—an integer or string. But the default case matches all other values. It is an "else" clause in the switch.

var number = 5;
// Use a default case in this switch.
switch (number) {
    case 4:
    console.log("FOUR");
    break;

    default:
    console.log("NOT FOUR");
}
NOT FOUR

Last break statement

In JavaScript the last break statement is not required. The last case statement will execute without a break and no errors will occur.

function test(value) {
    // No break statement is required on the last case.
    switch (value) {
        case 0:
        console.log("ZERO");
        break;
        case 1:
        console.log("ONE");
        break;
        case 2:
        console.log("TWO");
    }
}
test(0);
test(1);
test(2);
ZERO
ONE
TWO

Lookup tables

An object can be used instead of a switch statement to look up anonymous functions. We then call those functions. This appears to be slower than a switch statement.

With switch statements in Node.js, we have a way to test a variable and run code based on its value. This can make code more elegant and symmetrical.