LowFile-scopeJavaScript / TypeScript Plug & play

Classify HTTP errors with type-safe narrowing

Define a discriminated union or error class hierarchy and use user-defined type guards before handling specific cases.

Why this matters

Precise handling reduces brittle branches and unsafe casts.

Side-by-side examples engineers can pattern-match during review.

Avoid

catch(e){ if((e as any).status) retry(); }

Prefer

type HttpError={kind:'http',status:number,body?:unknown}; const isHttp=(x:unknown):x is HttpError=>!!x && (x as any).kind==='http';

Bad

if ((e as any).status) {}

Good

function isHttp(x:unknown): x is HttpError { /*...*/ }

From the same buckets as this rule.

Critical
Avoid equality operators in loop termination conditions
Check if loops use equality operators (== or !=) in termination conditions. These can lead to infinite loops if the condition is never met exactly. Instead, use relational operators like < or > for safer loop termination.
error-handlingreadability-refactor
Critical
Avoid Returning Null in Non-Async Task Methods
Returning null from a Task or Task<T> method causes a NullReferenceException if awaited. Use Task.CompletedTask or Task.FromResult<T>(null) instead.
error-handlingreadability-refactor+1
Critical
Avoid Using Boolean Expressions in `except` Statements
Detect `except` clauses that use `or` or `and` to catch multiple exceptions. This does not work as intended. Recommend using a tuple of exceptions instead.
error-handlingstack-python