Boy, wouldn’t that be nice. Too bad the Notepad++ Developer doesn’t have a budget and manpower of Microsoft-proportions helping him implement features. ;-)
BTW: HTML doesn’t have variables or functions. Are you really talking about the JavaScript embedded in an HTML document?
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Addendum: one of the power users here is currently working on developing an LSP (“Language Server Protocol”) client plugin for Notepad++: LSP is what Visual Studio uses for linking to various “LSP servers” which can give it augmented right-click and code-completion features that go beyond the code-completion that Notepad++ provides by default. Assuming that an LSP server exists for the language of your choice (his examples show ones for Python, V, and D; there might be one for HTML/JS/ASP/PHP/etc or some subset thereof). So once that plugin is ready for prime time, and if an LSP server existed for the combo of web technologies that you are programming for, you might be able to get some or all of the feature set you’re looking for (eventually).
Additionally, there are a variety of HTML and web-related plugins already available for Notepad++, and while waiting for the full features of LSP, some of those might help make your development easier.