title: How to add properties to a JSON in TypeScript?
body: <p>I have the following code:</p>
  <pre><code>type DailySummaryEntrry = {date: string, summary: ParsedSummary};
  
  function parseDailySummaries (summaries: DailyRawSummaries): DailySummaryEntrry[] {
    const entries: DailySummaryEntrry[] = [];
  
    for (const date in summaries) {
      const rawSummary = summaries[date];
      if (!rawSummary) continue;
      entries.date = date ;
      entries.summary= parseRawSummary(rawSummary);
    }
    return entries.sort().reverse(); // sort by newest date first
  }
  </code></pre>
  <p>I don't know why do I get</p>
  <p><code>Property 'date' does not exist on type 'DailySummaryEntrry[]'.deno-ts(2339)</code></p>
  <p>at this line
  <code>entries.date = date ;</code></p>
  <p>and:</p>
  <pre><code>Property 'summary' does not exist on type 'DailySummaryEntrry[]'.deno-ts(2339)
  </code></pre>
  <p>At this line</p>
  <pre><code>entries.summary= parseRawSummary(rawSummary);
  </code></pre>