Function prependTypeMapping

test/fixtures/snapshot/typescript.js:63331–63333

(source, target, mapper)

            return mapper1 ? makeCompositeTypeMapper(4 /* TypeMapKind.Merged */, mapper1, mapper2) : mapper2;
        }
        function prependTypeMapping(source, target, mapper) {
            return !mapper ? makeUnaryTypeMapper(source, target) : makeCompositeTypeMapper(4 /* TypeMapKind.Merged */, makeUnaryTypeMapper(source, target), mapper);
        }
        function appendTypeMapping(mapper, source, target) {
            return !mapper ? makeUnaryTypeMapper(source, target) : makeCompositeTypeMapper(4 /* TypeMapKind.Merged */, mapper, makeUnaryTypeMapper(source, target));
        }