<p dir="auto">Minor, but still:</p>
<div class="highlight highlight-source-ts notranslate position-relative overflow-auto" dir="auto" data-snippet-clipboard-copy-content="type nn = number;
class A {
    [s: nn]: number; // an error here, but it shouldn't be an error
}"><pre class="notranslate"><span class="pl-k">type</span> <span class="pl-smi">nn</span> <span class="pl-c1">=</span> <span class="pl-smi">number</span><span class="pl-kos">;</span>
<span class="pl-k">class</span> <span class="pl-smi">A</span> <span class="pl-kos">{</span>
    <span class="pl-kos">[</span><span class="pl-s1">s</span>: <span class="pl-smi">nn</span><span class="pl-kos">]</span>: <span class="pl-smi">number</span><span class="pl-kos">;</span> <span class="pl-c">// an error here, but it shouldn't be an error</span>
<span class="pl-kos">}</span></pre></div>
<div class="snippet-clipboard-content notranslate position-relative overflow-auto" data-snippet-clipboard-copy-content="type Guid = string;
var foo: { [deviceId: Guid]: DateTime } = {};"><pre class="notranslate"><code class="notranslate">type Guid = string;
var foo: { [deviceId: Guid]: DateTime } = {};
</code></pre></div>
<p dir="auto">Generates the error:</p>
<blockquote>
<p dir="auto">An index signature parameter type must be 'string' or 'number'.</p>
</blockquote>
<p dir="auto">It would be nice to be able to type indexes using string-aliases.</p>