eslint updates for Firefox developers

In the past week there has been quite a lot of progress made on the eslint front.

Last week I enabled the following rules for the default mozilla-central eslint configuration (/toolkit/.eslintrc.js):

• no-extra-label
• no-iterator
• no-regex-spaces
• no-self-assign
• no-unsafe-negation
• no-unused-labels
• object-shorthand
• brace-style
• no-multi-spaces
• no-debugger
• no-delete-var
• no-sparse-arrays
• no-unsafe-finally
• no-cond-assign
• no-extra-bind
• no-useless-call
• no-lone-blocks
• no-useless-return

Mark Banner has continued to work on fixing the remaining no-undef errors. This work is on-going and is being tracked by a meta bug.

Florian Quèze just landed a patch yesterday to simplify calls to Services.io.newURI so the two trailing arguments are optional. Previously 99% of the calls to the function passed in null for the trailing arguments. Florian is planning on cleaning up some addEventListener code as well and I am pushing for him to implement special eslint rules along with them to help enforce these changes going forward.

I enabled most of the rules for eslint and gathered counts of the number of errors related to each rule. The following list shows each disabled rule along with the number of associated errors as of mozilla-central revision f13abb8ba9f3:

• array-callback-return = 3
• no-new-func = 13
• no-useless-concat = 14
• no-void = 14
• no-multi-str = 15
• no-new-wrappers = 18
• no-array-constructor = 20
• no-eval = 20
• no-await-in-loop = 21
• no-sequences = 22
• no-inner-declarations = 23
• no-unmodified-loop-condition = 24
• wrap-iife = 25
• no-constant-condition = 28
• no-template-curly-in-string = 39
• no-loop-func = 44
• no-fallthrough = 51
• no-new = 56
• no-throw-literal = 134
• no-prototype-builtins = 158
• no-caller = 165
• no-unused-expressions = 171
• no-useless-escape = 194
• complexity = 208
• no-case-declarations = 238
• guard-for-in = 284
• radix = 342
• no-shadow = 356
• no-eq-null = 442
• dot-notation = 459
• default-case = 485
• block-scoped-var = 749
• no-empty-function = 1144
• dot-location = 2327
• no-extra-parens = 2464
• no-invalid-this = 2947

If you would like to work on fixing any of these, please file a bug in the Toolkit :: General component of Bugzilla and request review from myself, Mossop, or Standard8.

If you’d like eslint to run on a directory that you work in, remove the reference to it from the .eslintignore file located at the mozilla-central root and add a .eslintrc.js file. This will now allow eslint to scan that directory.

Also, another project that someone can pick up is to help us move towards a single rule definition. We would like to move to a single set of rules which will help for consistent coding styling. You can look at this listing of .eslintrc.js files to see the differences between them. Some define globals that are unique to the directory or have different include paths to the root configuration, but some also define extra rules. We would like to get those rules added to the root configuration, though we haven’t determined how to settle rule conflicts yet.