Using tern for error checking?

[rkistner]

Tern's type inference is amazing for auto-complete. Is it possible to use the same engine for error checking in JS?

It doesn't need to do syntax errors (which other tools such as JSHint can handle), but type errors like this:

var a = [];
var len = a.length();  // Error, since length is not a function

In the example above, Tern would know that a.length is an int, and cannot be called as a function.

I realize there could be false positives with difficult-to-detect cases whether e.g. the user defining/overriding functions/variables on prototypes. In my case I'm happy to ignore these.

Would it be possible to add functionality like this into Tern?

[marijnh]

It might be possible to create a Tern-like tool that does something like this, but it is not in the current scope of the project (and it would be tricky to get any kind of useful results on top of the current engine). I think something like TypeScript is a more promising approach here.

(Closing, since I have no plans to start adding such functionality.)

[angelozerr]

IMHO I think validation feature is the missing feature of tern. But I understand you have no time to support it. https://github.com/eslint/eslint based on esprima parser seems doing that. It is based on esprima parser. Perhaps it's interesting to study it to provide the same version with acorn+tern?

[angelozerr]

Jus for your information, I have created https://github.com/angelozerr/tern.lint project. It contains both tern lint plugin and CodeMirror lint addon which uses this tern lint plugin.

Any contribution are welcome!

[rkistner]

@angelozerr Looks great! I'll try it out later this week.

[angelozerr]

@rkistner pay attention, it's just a POC. Your original case with length() is not managed for instance.

Please create issues at https://github.com/angelozerr/tern.lint/issues to improve tern lint and any contribution are welcome!