Why does JSLint complain about “Unexpected ‘else’ after ‘return'”?

It’s just telling you that else after return is superfluous. The following is fine:

(function (x) {
    "use strict";
    if (x === 1) {
        return 1;
    }  
    if (x === 2) {
        return -1;
    }
    return 0;
}(1));