Improvements to JavaScript analysis

Changes to code extraction

Custom file types can now be specified using the filetypes property in the extraction/javascript/index section of lgtm.yml. The property should be a map from file extensions (including the dot) to file types. Valid file types are html, js, json, typescript, xml and yaml.
ECMAScript 2019 support is now enabled by default.
On LGTM, JavaScript extraction for projects that do not contain any JavaScript or TypeScript code will now fail, even if the project contains other file types (such as HTML or YAML) recognized by the JavaScript extractor.
XML files can now be extracted on LGTM. To enable XML extraction, set the xml_mode property in the extraction/javascript/index section of your lgtm.yml file to all. The default value of this property is disabled, meaning that XML files will not be extracted. (Note, that the xml_mode property does not apply to files that you map to the xml file type using the filetypes property. LGTM will always extract these files.)
YAML files are now extracted by default on LGTM. If required, you can specify exclusion filters in your lgtm.yml file to override this behavior.

For detailed information about customizing LGTM extraction, see JavaScript extraction.