statements.md

Statements

JavaScript statements perform actions but do not produce any value.

WTF

switch (42) {
    default:
        console.log('foo');
    case 10:
    case 20:
        console.log('bar');
        break;
    case 30:
        console.log('zed');
        break;
}
// foo
// bar

Why?

According to the specification, the default expression can be placed anywhere in the switch block. However, if we place it anywhere except in the last position (as shown in the example above) we will get some weird behaviour.

In this case, for our 42 example, the engine will go to all switch cases, skipping the default, and it will not find any match. At this point it will invoke the default clause and log foo. But because we didn't add a break statement after the default it will execute the following cases until it reaches a break. Therefore it will log bar.

Further Reading

Kyle Simpsons - What the... JavaScript? YouTube Video

WTF

function foo() {
    try {
        return 2
    } finally {
        return 3
    }
}

foo()   // 3

Why?

This happens because the result of evaluating the finally block is a return statement. Meaning that the result is the return completion of the expression followed (i.e. the expression 3).

However, by doing this, the result of the try block is overridden by the result of the finally block. Therefore explaining the final result of 3 when executing foo.

Further Reading

• [ECMAScript® 2015 Language Specification - The try Statement ] (https://www.ecma-international.org/ecma-262/6.0/index.html#sec-try-statement)