Re-write the rule about casting to be clearer (#26317)

This is the proposal from the comments on https://github.com/vector-im/element-web/pull/26220
(so effectively an alternative to that PR, if you like).
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David Baker 2023-10-09 14:34:36 +01:00 committed by GitHub
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@ -113,15 +113,17 @@ Unless otherwise specified, the following applies to all code:
}
```
14. Explicitly cast to a boolean, rather than relying on implicit truthiness of non-boolean values:
14. If a variable's type should be boolean, make sure it really is one.
```typescript
const isRealUser = !!userId && ...;
// ... or ...
const isRealUser = Boolean(userId) && ...;
const isRealUser = !!userId && ...; // good
const isRealUser = Boolean(userId) && Boolean(userName); // also good
const isRealUser = Boolean(userId) && isReal; // also good (where isReal is another boolean variable)
const isRealUser = Boolean(userId && userName); // also fine
const isRealUser = Boolean(userId || userName); // good: same as &&
const isRealUser = userId && ...; // bad: isRealUser is userId's type, not a boolean
// but *not*:
const isRealUser = userId && ...; // invalid implicit cast
if (userId) // fine: userId is evaluated for truthiness, not stored as a boolean
```
15. Use `switch` statements when checking against more than a few enum-like values.