Those methods were removed in the new format and should not be relied upon. This is useful for rules that need to check all comments regardless of location. Please note that the following methods have been deprecated and will be removed in a future version of ESLint:. The quotes rule in this example has one option, “double” the error is the error level. The above methods return a fixing object. Other possibilities The above example is something that was very convenient for our use case, but the possibilities are endless.

More information on writing custom EsLint rules can be found in the offical documentation. My name is Adrian and I work as a full stack developer at Webiny. If it is not included, should it be? Your engineering team has a strong preference about how to set something up, but others might choose a different option. The innermost scope is the module scope.

writing custom eslint rules

The fix function can return the following values:. To keep the linting process efficient and unobtrusive, it is useful to verify the performance impact of new rules or modifications to fustom rules.

writing custom eslint rules

The riles returns a simple object with methods as properties. It is followed by the first optional argument, a cystom which may be either “always” or “never”. Sign in Get started. Never miss a story from Flexport Engineeringwhen you sign up for Medium. The following example was copied from the AST explorer website, and it just prevents developers from using template literals. For others, we can use different libraries that we can port over as well when we port the application.


writing custom eslint rules

In either of these cases, the key is this: In order to analyze code we must first build an abstract syntax tree. EsLint is quite a nice alternative for JsHint and is very flexible.

You can do that like so:. The node contains all of the information necessary to figure out the line and column number of the offending text as well the source text representing the node.

First we need to know what part of the static tree cushom are going to lint.

Writing custom ESLint rules for your picky developers | Hacker News

If you have any questions or comments, feel free to reach out to me via Twitter. The next example shows some sample code and the corresponding syntax tree:.

Custom EsLint rules come in handy on a project-level basis. Not very useful maybe, but for demonstration purposes of this guide, it will suffice. Start by installing it and the generator: Thanks for the help!

Working with Rules

Sometimes writing a custom rule makes sense, but it should be an exception and not the rule. This will install the package from the local folder my-eslint-plugin. This can then custoj plugged in to EsLint and it will report the errors for any Javascript code you throw at it.

There are a couple of reasons: Finally, just npm install and you have yourself a plugin! Additionally, the context object has the following methods:. This allows you to avoid retyping error messages. This syntax will allow us to install a eriting that is on our local file system.


The SourceCode object is the main object for getting more information about the source code being linted. This custtom useful for rules that need to check all comments regardless of location. When the rule identifies that the code represented by the AST is in violation of the rule that is being enforced, it simply must call context.

Create custom ESLint rules in 2 minutes – Webiny Blog

You can retrieve the SourceCode object at any time by using the getSourceCode method:. For example, the yoda rule accepts a primary mode argument, as well as an extra options object with named properties.

There are dozens upon dozens of plugins and examples out there with more complex examples; see eslint-plugin-react for some really good ones. Omit the fixable property if the rule is not fixable. Tools help you get the job done, not get in the way. The above visualization can also be presented as a pure data structure, wrtiing in the form of JSON:.