# no-unsafe-finally

Forbid the use of unsafe control flow statements in try and catch blocks.

JavaScript suspends any running control flow statements inside of try and catch blocks until finally is done executing. This means that any control statements such as return, throw, break, and continue which are used inside of a finally will override any control statements in try and catch. This is almost always unexpected behavior.

# Incorrect Code Examples

// We expect 10 to be returned, but 5 is actually returned
function foo() {
    try {
        return 10;
    //  ^^^^^^^^^ this statement is executed, but actually returning is paused...
    } finally {
        return 5;
    //  ^^^^^^^^^ ...finally is executed, and this statement returns from the function, **the previous is ignored**
    }
}
foo() // 5

Throwing errors inside try statements

// We expect an error to be thrown, then 5 to be returned, but the error is not thrown
function foo() {
    try {
        throw new Error("bar");
    //  ^^^^^^^^^^^^^^^^^^^^^^^ this statement is executed but throwing the error is paused...
    } finally {
        return 5;
    //  ^^^^^^^^^ ...we expect the error to be thrown and then for 5 to be returned,
    //  but 5 is returned early, **the error is not thrown**.
    }
}
foo() // 5
More incorrect examples
try {
    throw A;
} finally {
    return;
}
try {
    throw new Error();
} catch {

} finally {
    continue;
}
More correct examples
try {
    throw A;
} finally {
    if (false) {
        return true;
    }
}

Source (opens new window)

Last Updated: 11/18/2020, 9:36:33 PM