Function speculationHelper

test/fixtures/snapshot/typescript.js:12229–12248

(callback, isLookahead)

            }
        }
        function speculationHelper(callback, isLookahead) {
            var savePos = pos;
            var saveStartPos = startPos;
            var saveTokenPos = tokenPos;
            var saveToken = token;
            var saveTokenValue = tokenValue;
            var saveTokenFlags = tokenFlags;
            var result = callback();
            // If our callback returned something 'falsy' or we're just looking ahead,
            // then unconditionally restore us to where we were.
            if (!result || isLookahead) {
                pos = savePos;
                startPos = saveStartPos;
                tokenPos = saveTokenPos;
                token = saveToken;
                tokenValue = saveTokenValue;
                tokenFlags = saveTokenFlags;
            }
            return result;
        }
        function scanRange(start, length, callback) {
            var saveEnd = end;
            var savePos = pos;