How to use the @microsoft/recognizers-text.StringUtility.isWhitespace function in @microsoft/recognizers-text

chars.forEach(c => {
            let codePoint = c.codePointAt(0) || c.charAt(0);
            if (codePoint > 0xFFFF) {
                // Character is in a Supplementary Unicode Plane. This is where emoji live so
                // we're going to just break each character in this range out as its own token.
                tokens.push(c);
                if (!StringUtility.isNullOrWhitespace(token)) {
                    tokens.push(token);
                    token = '';
                }
            }
            else if (!(this.config.tokenRegex.test(c) || StringUtility.isWhitespace(c))) {
                token = token.concat(c);
            }
            else if (!StringUtility.isNullOrWhitespace(token)) {
                tokens.push(token);
                token = '';
            }
        });

let suffix = afterStr.substr(match.index + match.length).trim();

                        let endingMatch = RegExpUtility.getMatches(this.config.generalEndingRegex, suffix).pop();
                        if (endingMatch) {
                            tokens.push(new Token(er.start || 0, er.start + er.length + match.index + match.length || 0));
                        }
                    }
                }
            }

            let beforeStr = source.substr(0, er.start);
            match = RegExpUtility.getMatches(this.config.periodTimeOfDayWithDateRegex, beforeStr).pop();
            if (match) {
                if (StringUtility.isNullOrWhitespace(beforeStr.substr(match.index + match.length))) {
                    let middleStr = source.substr(match.index + match.length, er.start - match.index - match.length);
                    if (StringUtility.isWhitespace(middleStr)) {
                        tokens.push(new Token(match.index, er.start + er.length));
                    }
                }
                else {
                    let pauseMatch = RegExpUtility.getMatches(this.config.middlePauseRegex, beforeStr.substr(match.index + match.length)).pop();

                    if (pauseMatch) {
                        // TODO: should use trimStart() instead?
                        let suffix = source.substr(er.start + er.length || 0).trim();

                        let endingMatch = RegExpUtility.getMatches(this.config.generalEndingRegex, suffix).pop();
                        if (endingMatch) {
                            tokens.push(new Token(match.index, er.start + er.length || 0));
                        }

                    }