See: [Walkthrough: Interfaces | TypeScript :: Describing Simple Types](https://blogs.msdn.microsoft.com/typescript/2013/01/24/walkthrough-interfaces/#Subsection_64).

Basically, `?` marks the member as being optional in the interface.

(EDIT: As noted in comments, this is not restricted to interfaces.)

In this case, the `?:` is not a single operator, but rather two operators:

 - `?` (optional),

 - `:` (specify type).

In other languages/cases, `?:` would be [the Elvis Operator](https://en.wikipedia.org/wiki/Elvis_operator).

I am trying to update a value in the nested array but can&#39;t get it to work.

My object is like this

     {
        &quot;_id&quot;: {
            &quot;$oid&quot;: &quot;1&quot;
        },
        &quot;array1&quot;: [
            {
                &quot;_id&quot;: &quot;12&quot;,
                &quot;array2&quot;: [
                      {
                          &quot;_id&quot;: &quot;123&quot;,
                          &quot;answeredBy&quot;: [],   // need to push &quot;success&quot; 
                      },
                      {
                          &quot;_id&quot;: &quot;124&quot;,
                          &quot;answeredBy&quot;: [],
                      }
                 ],
             }
         ]
     }

I need to push a value to &quot;answeredBy&quot; array.

In the below example, I tried pushing &quot;success&quot; string to the &quot;answeredBy&quot; array of the &quot;123 _id&quot; object but it does not work.


    callback = function(err,value){
         if(err){
             res.send(err);
         }else{
             res.send(value);
         }
    };
    conditions = {
        &quot;_id&quot;: 1,
        &quot;array1._id&quot;: 12,
        &quot;array2._id&quot;: 123
      };
    updates = {
       $push: {
         &quot;array2.$.answeredBy&quot;: &quot;success&quot;
       }
    };
    options = {
      upsert: true
    };
    Model.update(conditions, updates, options, callback);

I found this [link][1], but its answer only says I should use object like structure instead of array&#39;s. This cannot be applied in my situation.  I really need my object to be nested in arrays 

It would be great if you can help me out here. I&#39;ve been spending hours to figure this out.

Thank you in advance!

  [1]: https://stackoverflow.com/questions/4121666/updating-nested-arrays-in-mongodb

Updating a Nested Array with MongoDB

I am writing tests for my site using Selenium IDE and I am having trouble with having selenium click on a button using preceding-sibling

    &lt;td&gt;
    &lt;div class=&quot;btn-group&quot;&gt;
    &lt;button class=&quot;btn btn btn-danger block&quot; title=&quot;Warning, Delete&quot; name=&quot;delete&quot; type=&quot;button&quot;&gt;
    &lt;button class=&quot;btn btn btn-default block&quot; title=&quot;View History&quot; name=&quot;history&quot; type=&quot;button&quot;&gt;
    &lt;button class=&quot;btn btn btn-default block&quot; title=&quot;View Settings&quot; name=&quot;settings&quot; type=&quot;button&quot;&gt;
    &lt;button class=&quot;btn btn btn-default block&quot; name=&quot;device&quot; type=&quot;button&quot;&gt;
    &lt;span class=&quot;glyphicon glyphicon-pencil&quot;/&gt;
     Arcade Reader
    &lt;/button&gt;
    &lt;/div&gt;
    &lt;/td&gt;
My path

    xpath=//button[contains(.,&#39;Arcade Reader&#39;)]/../preceding-sibling::button[@name=&#39;settings&#39;]

How to use XPath preceding-sibling correctly

I found the following in a TypeScript declaration file for Angular:

    interface IDirective{
        compile?:
            (templateElement: IAugmentedJQuery,

What does the `?:` after compile do? 

What does ?: mean in Typescript?

I found the following in a TypeScript declaration file for Angular:
<pre><code class="hljs language-csharp">interface IDirective{
 compile?:
 (templateElement: IAugmentedJQuery,
</code></pre>
What does the <code>?:</code> after compile do?

I&#39;m using TypeScript for a reasonably large project, and am wondering what the standard is for the use of `Error`s. For example, say I hand an index out of bounds exception in Java:

    throw new IndexOutOfBoundsException();

Would the equivalent statement in TypeScript be:

    throw new Error(&quot;Index Out of Bounds&quot;);

What other ways could I accomplish this? What is the accepted standard?

Proper use of errors

I found a lot of examples and also tried myself to split a module into several files. So I get that one, very handy. But it&#39;s also practical sometimes to split a class for the same reason. Say I have a couple of methods and I don&#39;t want to cram everything into one long file.

I&#39;m looking for something similar to the **partial** declaration in C#.

How do I split a TypeScript class into multiple files?

Maybe it&#39;s obvious, but I checked everywhere (besides the right place) and googled it. Nothing.

Where can I find the TypeScript version installed in Visual Studio?

I am new to typescript and am trying to understand how I can setup a circular reference between two types.  The reference need not be a full code reference, simply the interfaces, but with interfaces defined in separate files.  For example, let&#39;s say I have two interfaces: Parent and Child.  They are doubly-linked such that the parent has a collection of children and each child has a reference to the parent (as seen below).  How do I setup the imports or dependencies so that these can be defined in separate files?

    interface Parent {
      children: Child[]
    }

    interface Child {
      parent: Parent
    }

Circular Type References in TypeScript

Content Type	Original Author	Original Content on Stackoverflow
Question	Erik Z	View Question on Stackoverflow
Solution 1 - Typescript	Amadan	View Answer on Stackoverflow
Solution 2 - Typescript	KarolDepka	View Answer on Stackoverflow

What does ?: mean in Typescript?

Typescript Problem Overview

Typescript Solutions

Solution 1 - Typescript

Solution 2 - Typescript

How to use XPath preceding-sibling correctly

Updating a Nested Array with MongoDB

Attributions