# `deslop/simplifiable-expression`

Disallow expressions that collapse to a simpler equivalent, e.g. !!x → Boolean(x).

- **Category:** Correctness
- **Severity:** warn
- **Source:** deslop-js
- **Framework:** global
- **Enabled when:** react-doctor deadCode analysis enabled (default true); whole-project scan only — skipped in --diff/--staged modes
- **Documentation:** <https://github.com/millionco/deslop-js>

## Validation prompt

Use this to decide whether a fired diagnostic is real or a false positive.

Fires when deslop's simplifiable-expression detector matches one of five AST shapes and emits a reason/suggestion: self-fallback-ternary (test text equals consequent text, reason `x ? x : y` is a self-fallback ternary), ternary-returns-boolean (`cond ? true : false` collapses to `Boolean(cond)` / `cond ? false : true` collapses to `!cond`), double-bang-boolean (`!!x` is a double-negation boolean coercion), nullish-coalescing-with-nullish (`x ?? null` or `x ?? undefined`), or redundant-null-and-undefined-check (`x !== null && x !== undefined` is equivalent to `x != null`). False positive: the nullish-coalescing-with-nullish case is often intentional — deslop's own reason flags that `x ?? null` may be required by a caller's signature (PropTypes, a form-control onChange that demands `null` not `undefined`) where the `?? null` coercion changes the resolved type; also rare cases where a `!!x` is kept as an explicit, readable boolean coercion at a JSX render guard like `{!!items.length && <List/>}` (still generally worth simplifying). Suppress when the coercion is load-bearing for a downstream type or contract; otherwise confirm.

## Fix prompt

Use this once validation confirms the diagnostic is real.

Apply deslop's suggestion for the matched kind: rewrite `cond ? true : false` to `Boolean(cond)` (or just `cond` when the type already is boolean) and `cond ? false : true` to `!cond`; rewrite `!!x` to `Boolean(x)`; collapse `x !== null && x !== undefined` to `x != null`; and rewrite a self-fallback `x ? x : y` to `x ?? y` (nullish-only) or `x || y` (falsy fallback) per intent. For `x ?? null`/`x ?? undefined`, only drop the `?? null` when `x` is already typed `T | null` (the coalesce is then a no-op); if the literal is required to satisfy a prop or callback signature, keep it. These are behavior-preserving simplifications that remove noise and signal intent more directly. See https://github.com/millionco/deslop-js