CodeSOD: Adding to the Argument

David G saw a pull request with a surprisingly long thread of comments on it. What was weirder was that the associated ticket was all about adding a single parameter to an existing method. What could be generating that much discussion?

How could adding an argument add to an argument?

<span class="hljs-attr">registerFooWrapper</span>: <span class="hljs-keyword">function</span>(<span class="hljs-params">arg1, arg2, arg3, arg4, arg5, arg6, arg7</span>) {
    bar.<span class="hljs-title function_">when</span>(<span class="hljs-string">'bar-event'</span>, <span class="hljs-keyword">function</span>(<span class="hljs-params">context</span>) {
        context.<span class="hljs-title function_">foo</span>({
            <span class="hljs-attr">arg1</span>: arg1,
            <span class="hljs-attr">arg2</span>: arg2,
            <span class="hljs-attr">arg3</span>: arg3,
            <span class="hljs-attr">arg4</span>: arg4,
            <span class="hljs-attr">arg5</span>: arg5,
            <span class="hljs-attr">arg6</span>: arg6,
            <span class="hljs-attr">arg7</span>: arg7,
        });
    });
}

This is the original version of the JavaScript function. The parameter names have been anonymized. That aside, this still isn’t very good. Seven parameters is likely too many, and based on what I see in setting the context, there is an object type that holds them all, so maybe we should be passing the object around in the first place? Still, this isn’t a WTF by any stretch, and since it’s already deployed code, changing the interface significantly is a bad idea- maybe just adding a parameter is the right choice here. So what generated so much discussion?

This revision:

<span class="hljs-attr">registerFooWrapper</span>: <span class="hljs-keyword">function</span>(<span class="hljs-params">arg1, arg2, arg3, arg4, arg5, arg6, arg7, notArg8</span>) {
    <span class="hljs-keyword">if</span> (notArg8 === <span class="hljs-literal">true</span>) {
        bar.<span class="hljs-title function_">when</span>(<span class="hljs-string">'bar-event'</span>, <span class="hljs-keyword">function</span>(<span class="hljs-params">context</span>) {
            context.<span class="hljs-title function_">foo</span>({
                <span class="hljs-attr">arg1</span>: arg1,
                <span class="hljs-attr">arg2</span>: arg2,
                <span class="hljs-attr">arg3</span>: arg3,
                <span class="hljs-attr">arg4</span>: arg4,
                <span class="hljs-attr">arg5</span>: arg5,
                <span class="hljs-attr">arg6</span>: arg6,
                <span class="hljs-attr">arg7</span>: arg7,
                <span class="hljs-attr">arg8</span>: !notArg8,
            });
        });
    }
    <span class="hljs-keyword">else</span> {
        bar.<span class="hljs-title function_">when</span>(<span class="hljs-string">'bar-event'</span>, <span class="hljs-keyword">function</span>(<span class="hljs-params">context</span>) {
            context.<span class="hljs-title function_">foo</span>({
                <span class="hljs-attr">arg1</span>: arg1,
                <span class="hljs-attr">arg2</span>: arg2,
                <span class="hljs-attr">arg3</span>: arg3,
                <span class="hljs-attr">arg4</span>: arg4,
                <span class="hljs-attr">arg5</span>: arg5,
                <span class="hljs-attr">arg6</span>: arg6,
                <span class="hljs-attr">arg7</span>: arg7
            });
        });
    }
}

Okay, so if notArg8 is true, we pass false to the context. If it’s any other value, we don’t past arg8 at all. I do not understand what I’m looking at here. If the goal is to ensure that arg8 is either true or not set, there are clearer ways to express that idea. But also, the goal of the ticket was not to do that- it was simply to add another parameter, which means you could drop the condition entirely and just add the parameter. context was already receiving arg8 as undefined, so it could clearly handle an undefined value.

David made some comments on the pull request, but the original developer just ended up going radio silent on it. One of the juniors on David’s team approved it, for some reason, but nobody ever actually hit merge. Instead, a different developer simply made a version that took arg8 as a parameter, passed it down to context, and called it a day. It worked, the tests passed, and everyone was happy.

Well, except the original developer, but again, who knows what they were trying to do?

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