Custom eslint rules
Valeriy Kuzmin,
Lilt, 2020
The little problem
The actual problem
// @typescript-eslint/explicit-module-boundary-types
// no error !!!
module.exports.myFunc = (arg1: number, arg2,
arg3: boolean) => {
...
}
// an error
export const myFunc = (arg1: number, arg2,
arg3: boolean) => {
...
}
The grand problem
JS
TS
The grand problem
The restrictions
- Humans are not really scalable
- The knowledge is not uniform
- It's damn hard to do manually
- Product needs to be developed
- We have a ton of bad code
The answer
Automation! Tons of it.
The grand strategy
Rule 1: use TS & Eslint
Rule 2: boundaries
Rule 3: no problematic code
Time
Abstract Syntax Tree
- Your code is data!
- astexplorer.net
- @typescript-eslint/parser
a + b
Binarry expression
Operator +
Left:
variable a
Right:
variable b
Abstract Syntax Tree
module.exports = 456;
Visitors
AssignmentExpression(node) {
try {
if (
_.get(node, "left.object.name") === "module" ||
_.get(node, "left.object.property.name") === "exports" ||
_.get(node, "left.object.name") === "exports" ||
_.get(node, "left.name") === "exports"
) {
context.report({ messageId: "noModuleInTsError", node });
}
} catch (error) {
context.report({
node,
messageId: "unknownError"
});
}
}
};
Apparently our version of parser is a bit buggy, hence _.get
A good rule
- Description
- Sensible error text
- Suggestion what to do
- Tests
- Added to our config
- File exceptions if needed
- Auto-fix
.eslintrc.js:
"local-rules/no-module-in-ts": 2
eslint-local-rules.js:
"no-module-in-ts": require("./libs/eslint/rules/no-module-in-ts").default
Profit
- I don't need to look for this in PRs
- Criticism from robots is better
- We have a template and can make more rules
- TS is enforced better
- We can go further!
What's next?
- Automatic fixes for code via eslint. Easier progression of the grand plan.
- JSCodeShift transforms for auto-refactoring. E.g. then → await
- Much more specialized rules, unique for our codbase
Call to action
My personal CTA: no rule exceptions in .eslintrc, only inside files (item 2 in the form)
Thanks!
Questions?
custom-eslint-at-lilt
By Valeriy Kuzmin
custom-eslint-at-lilt
- 247