tests/cases/compiler/downlevelLetConst19.ts(9,14): error TS1250: Function declarations are not allowed inside blocks in strict mode when targeting 'ES3' or 'ES5'. ==== tests/cases/compiler/downlevelLetConst19.ts (1 errors) ==== 'use strict' declare function use(a: any); var x; function a() { { let x; use(x); function b() { ~ !!! error TS1250: Function declarations are not allowed inside blocks in strict mode when targeting 'ES3' or 'ES5'. { let x; use(x); } use(x); } } use(x) } use(x)