@fimbul/mimir

Mímir

Core rules, formatters and configurations of the Fimbullinter project.

Make sure to also read the full documentation of all available modules.

Purpose

This library contains all core rules, formatters and configuration presets of the Fimbullinter project. As a typical user you don't need to explicitly install this package. It's already installed as a dependency of Wotan.

Rules

Rule	Description	Difference to TSLint rule / Why you should use it
await-async-result	:mag: Warns about not using the result of a call to an async function inside async functions.	TSLint's no-floating-promises requires you to specify a list of Promise names, it checks outside of async functions and only requires you to register the onrejected callback.
await-only-promise	:mag: :wrench: Finds uses of await on non-Promise values. Also checks for await loops.	Works for all PromiseLike and Thenable types out of the box without any configuration.
ban-dom-globals	:mag: Disallows uses of global variables like name or event. Using these variables is most likely not intended.	There's an open PR to add a similar rule to TSLint.
generator-require-yield	Requires at least one yield inside generator functions.	There's no similar TSLint rule.
new-parens	:wrench: Requires parentheses when invoking constructors.	Performance!
no-case-declaration	Disallows let, class and enum in case blocks.	TSLint has no similar rule, ESLint has no-case-declarations which forbids function declarations as well.
no-debugger	:wrench: Bans debugger; statements from your production code.	Performance!
no-duplicate-case	:mag_right: Detects switch statements where multiple case clauses check for the same value.	This implementation tries to infer the value instead of just comparing the source code.
no-duplicate-spread-property	:mag: Detects properties in object literals with object spread that are always overridden.	TSLint has no such rule.
no-fallthrough	Prevents unintentional fallthough in switch statements from one case to another.	Allows more comment variants such as fallthrough or fall through.
no-inferred-empty-object	:mag: Detects type parameters that are inferred as {} because the compiler cannot infer a type.	Really checks every type parameter of function, method and constructor calls. Correctly handles type parameters from JSDoc comments. Recognises type parameter defaults on all merged declarations.
no-invalid-assertion	:mag: Disallows asserting a literal type to a different literal type of the same widened type, e.g. 'foo' as 'bar'.	TSLint has no similar rule.
no-misused-generics	Detects generic type parameters that cannot be inferred from the functions parameters. It also detects generics that don't enforce any constraint between types.	There's no similar TSLint rule.
no-nan-compare	Disallows comparing with NaN, use isNaN(number) or Number.isNaN(number) instead.	Performance!
no-return-await	Disallows unnecesary return await foo; when you can simply return foo;	The same as TSLint's rule. I wrote both, but this one is faster.
no-unassigned-variable	Detects variables that are not initialized and never assigned a value.	There's no similar TSLint rule.
no-unreachable-code	Warns about statements that will never be executed. Works like TypeScript's dead code detection but doesn't fail compilation because it's a lint error.	TSLint removed their no-unreachable rule in v4.0.0.
no-unsafe-finally	Forbids control flow statements return, throw, break and continue inside the finally block of a try statement.	Performance!
no-unstable-api-use	Finds uses of deprecated and experimental variables, classes, properties, functions, signatures, ... requires type information	This rule checks element accesses (foo[bar]), JSX elements, chained function calls (getFn()()) in addition to what TSLint's deprecation rule does and has more useful error reporting.
no-unused-expression	Warns about side-effect free expressions whose value is not used	This one is a bit stricter than TSLint's no-unused-expression and checks for loops in addition.
no-unused-label	Warns about labels that are never used or at the wrong position.	TSLint only has label-position which doesn't check for unused labels.
no-useless-assertion	Detects type assertions that don't change the type or are not necessary in the first place. requires type information	TSLint's no-unnecessary-type-assertion does not detect assertions needed to silence the compiler warning Variable ... is used before being assigned. The Wotan builtin rule also checks whether the assertion is necessary at all or the receiver accepts the original type.
no-useless-declare	Disallows the declare keyword on statements without runtime value, e.g. declare type T = any;.	TSLint has no such rule.
no-useless-initializer	Detects unnecessary initialization with undefined and destructuring defaults (requires type information).	TSLint's rule no-unnecessary-initializer doesn't fix all parameter initializers and gives false positives for destructuring.
no-useless-jump-label	Detects continue label; and break label; where the label is not necessary.	There's no similar TSLint rule.
no-useless-predicate	Detects redundant conditions that are either always true or always false. requires type information	Combination of TSLint's strict-type-predicates, typeof-compare and parts of strict-boolean-expressions.
no-useless-spread	Detects redundant array and object spread which can safely be removed.	There's no similar TSLint rule.
prefer-const	Prefer const for variables that are never reassigned. Use option {destructuring: "any"} if you want to see failures for each identifier of a destructuring, even if not all of them can be constants. The default is {destructuring: "all"}.	TSLint's prefer-const rule gives some false positives for merged declarations and variables used in before being declared which results in a compiler error after fixing.
prefer-dot-notation	Prefer obj.foo over obj['foo'] where possible.	Same as TSLint's no-string-literal rule, but more performant.
prefer-for-of	Prefer for-of loops over regular for loops where possible. requires type information	Avoids the false positives of TSLint's prefer-for-of rule.
prefer-namespace-keyword	Prefer namespace foo {} over module foo {} to avoid confusion with ECMAScript modules.	Same as TSLint's no-internal-module.
prefer-number-isnan	Prefer ES2015's Number.isNaN over the global isNaN mainly for performance. requires type information	No similar rule in TSLint.
prefer-object-spread	Prefer object spread over Object.assign for copying properties to a new object. requires type information	Performance, and better handling of parens in fixer and avoids false positives that would cause a compile error when fixed.
return-never-call	Prefer return neverReturns(); or throw neverReturns(); over plain calls to neverReturns(); to enable better control flow analysis and type inference.	TSLint has no similar rule.
syntaxcheck	Reports syntax errors as lint errors. This rule is not enabled in wotan:recommended. requires type information	Used to be part of the deprecated tslint --type-check
trailing-newline	Requires a line break at the end of each file.	Nothing fancy here :(
try-catch-return-await	Companion of no-return-await because inside a try-catch block you should await returned promises to correctly enter the catch on rejection and/or the finally block after completion. requires type information	TSLint has no similar rule.
typecheck	TypeScript's compiler errors as lint errors. This rule is not enabled in wotan:recommended. requires type information	Like the deprecated tslint --type-check but formatted and can be disabled like any other rule.

Formatters

• stylish
• json

Configuration Presets

• wotan:recommended contains recommended builtin rules. This configuration only adds new rules in major versions.
• wotan:latest contains recommended builtin rules and is updated in minor versions. Be aware that this might cause your build to break.

License

Apache-2.0 © Klaus Meinhardt

Changelog

v0.9.0

Features:

• new rule: parameter-properties (contributed by @aervin)
• new rule: no-duplicate-spread-property
• new rule: prefer-namespace-keyword
• new rule: no-useless-declare
• new rule: ban-dom-globals
• bifrost added a function to wrap Fimbullinter rules for the use in TSLint
• many rules now have a detailed documentation page
• Node.js v10 is now officially supported

Bugfixes:

• await-only-promise now allows for-await-of with Iterable<PromiseLike<any>>, previously it only allowed AsyncIterable<any>
• no-duplicate-case added check for unions of literal types
• no-inferred-empty-object handles generic functions declared in JSDoc
• no-useless-assertion fixed detection if variable may be used before being assigned and thus the non-null assertion is actually necessary