Rule idea: detect code duplication

I’d like eslint to produce a warning when I have pieces of duplicated code.

Precisely, I’d like no n- (default 3) line chunk to be repeated more then k (default 2) times. If it happens, the k+1-th occurrence should trigger a warning: “These n lines are duplicated for k+1-th time”.

Quite possibly we will also need to only take into account lines containing alpha-numeric characters, because we don’t want to detect chunks like:

    return this;
},
<empty line>

This rule does not prevent errors, but helps maintain overall code quality. I think that (in its simplest version) it’s generic enough to be useful for any code, regardless of JS dialect or framework.

Do you think it’s a good idea to have this rule in core ESLint, or shall it be a plugin?

[lo1tuma]

ESLint rules only operate on the context of a single file. So you won’t be able to detect duplicated code across multiple files.

I suggest to use tools like jscpd or jsinspect.

[nzakas]

As @lo1tuma suggested, this isn’t an area where ESLint is the best tool, as each file is looked at separately.