How to use the ts-util-is.isString function in ts-util-is

function getConns(config) {
    if (config.connection) {
        // deprecated (v1.1.0)
        console.warn(chalk_1.default.yellow('Warning! The config `connection` object is deprecated. Use `connections` instead.'));
        var legacyConn = config.connection;
        config.connections = (ts_util_is_1.isString(legacyConn) ? legacyConn : [legacyConn]);
    }
    if (ts_util_is_1.isString(config.connections)) {
        // get form web config
        return getWebConfigConns(config.connections);
    }
    else {
        return config.connections;
    }
}
exports.getConns = getConns;

function getConns(config) {
    if (config.connection) {
        // deprecated (v1.1.0)
        console.warn(chalk_1.default.yellow('Warning! The config `connection` object is deprecated. Use `connections` instead.'));
        var legacyConn = config.connection;
        config.connections = (ts_util_is_1.isString(legacyConn) ? legacyConn : [legacyConn]);
    }
    if (ts_util_is_1.isString(config.connections)) {
        // get form web config
        return getWebConfigConns(config.connections);
    }
    else {
        return config.connections;
    }
}
exports.getConns = getConns;

getConnections() {
    if (!isString(this.connections)) {
      return this.connections;
    }

    const configFile = /\.config$/;

    if (configFile.test(this.connections)) {
      return Config.getConnectionsFromWebConfig(this.connections);
    } else {
      return this.getConnectionsFromJson(this.connections);
    }
  }

private safeValue(value: any): any {
    if (isNull(value)) {
      return 'NULL';
    }

    if (isString(value)) {
      value = value.replace("'", "''");
      return `'${value}'`;
    }

    if (isDate(value)) {
      value = value.toISOString();
      return `'${value}'`;
    }

    if (isBoolean(value)) {
      return value ? 1 : 0;
    }

    return value;
  }

function safeValue(value: any): any {
  if (isString(value)) {
    value = value.replace("'", "''");
    return `'${value}'`;
  }

  if (isDate(value)) {
    value = value.toISOString();
    return `'${value}'`;
  }

  if (isBoolean(value)) {
    return value ? 1 : 0;
  }

  return value;
}