swc/crates/swc_ecma_parser/tests/tsc/controlFlowAliasingCatchVariables.ts

// @useUnknownInCatchVariables: true,false

try {}
catch (e) {
    const isString = typeof e === 'string';
    if (isString) {
        e.toUpperCase(); // e string
    }

    if (typeof e === 'string') {
        e.toUpperCase(); // e string
    }
}

try {}
catch (e) {
    const isString = typeof e === 'string';

    e = 1;

    if (isString) {
        e.toUpperCase(); // e any/unknown
    }

    if (typeof e === 'string') {
        e.toUpperCase(); // e string
    }
}