How to route EVERYTHING other than Web API to /index.html

Use a wildcard segment:

routes.MapRoute(    name: "Default",    url: "{*anything}",    defaults: new { controller = "Home", action = "Index" });

Suggest more native approach

<system.webServer>    <httpErrors errorMode="Custom">        <remove statusCode="404" subStatusCode="-1"/>        <error statusCode="404" prefixLanguageFilePath="" path="/index.cshtml" responseMode="ExecuteURL"/>    </httpErrors></system.webServer>

in my case none of these approaches worked. i was stuck in 2 error message hell. either this type of page is not served or some sort of 404.

url rewrite worked:

<system.webServer>    <rewrite>      <rules>        <rule name="AngularJS" stopProcessing="true">          <match url="[a-zA-Z]*" />          <conditions logicalGrouping="MatchAll">            <add input="{REQUEST_FILENAME}" matchType="IsFile" negate="true" />            <add input="{REQUEST_FILENAME}" matchType="IsDirectory" negate="true" />            <add input="{REQUEST_URI}" pattern="^/(api)" negate="true" />          </conditions>          <action type="Rewrite" url="/" />        </rule>      </rules>    </rewrite>    ...

notice i matched on [a-zA-Z] because i don't want to rewrite any of the .js .map etc urls.

this worked in VS out of hte box, but in IIS you may need to install a url-rewrite module https://www.iis.net/downloads/microsoft/url-rewrite