UglifyJS/test/compress/dead-code.js

dead_code_1: {
    options = {
        dead_code: true
    };
    input: {
        function f() {
            a();
            b();
            x = 10;
            return;
            if (x) {
                y();
            }
        }
    }
    expect: {
        function f() {
            a();
            b();
            x = 10;
            return;
        }
    }
}

dead_code_2_should_warn: {
    options = {
        dead_code: true
    };
    input: {
        function f() {
            g();
            x = 10;
            throw "foo";
            // completely discarding the `if` would introduce some
            // bugs.  UglifyJS v1 doesn't deal with this issue; in v2
            // we copy any declarations to the upper scope.
            if (x) {
                y();
                var x;
                function g(){};
                // but nested declarations should not be kept.
                (function(){
                    var q;
                    function y(){};
                })();
            }
        }
    }
    expect: {
        function f() {
            g();
            x = 10;
            throw "foo";
            var x;
            function g(){};
        }
    }
}

dead_code_constant_boolean_should_warn_more: {
    options = {
        dead_code    : true,
        loops        : true,
        booleans     : true,
        conditionals : true,
        evaluate     : true
    };
    input: {
        while (!((foo && bar) || (x + "0"))) {
            console.log("unreachable");
            var foo;
            function bar() {}
        }
        for (var x = 10, y; x && (y || x) && (!typeof x); ++x) {
            asdf();
            foo();
            var moo;
        }
    }
    expect: {
        var foo;
        function bar() {}
        // nothing for the while
        // as for the for, it should keep:
        var x = 10, y;
        var moo;
    }
}

dead_code_block_decls_die: {
    options = {
        dead_code    : true,
        conditionals : true,
        booleans     : true,
        evaluate     : true
    };
    input: {
        if (0) {
            let foo = 6;
            const bar = 12;
            class Baz {};
            var qux;
        }
        console.log(foo, bar, Baz);
    }
    expect: {
        var qux;
        console.log(foo, bar, Baz);
    }
}