parseDate function is not working as expected when used in Bigquery UDF

[ted-ks]

I had a use case to use chrono in my Bigquery models via UDFs. I have made the setup to import the chrono library and use it from my sql scripts. I am facing an issue with parseDate function when I pass a referenceDate along with date text.

for eg.

let testDate = new Date("2025-06-07")
let testText = "1 day ago"
const parsedDate = chrono.parseDate(periodText, refDate);

If I run the above code, parsedDate is always returning the previous day's date from current date instead of "2025-06-06" in Bigquery, If I run the same in a chrome console it works as expected. In a different realm it is causing issue.

export class ReferenceWithTimezone {
    readonly instant: Date;
    readonly timezoneOffset?: number | null;

    constructor(input?: ParsingReference | Date) {
        input = input ?? new Date();
        if ( input instanceof Date ) {. // COMMENT : This always returns false. 
            this.instant = input;
            this.timezoneOffset = null;
        } else {
            this.instant = input.instant ?? new Date();
            this.timezoneOffset = toTimezoneOffset(input.timezone, this.instant);
        }
    }
    // skip
}

input instanceof Date this statement always return false in bigquery.

I was able to get my use case working after modifying my function as follows, but wondering whether the multiple realm fix is feasible (Object.prototype.toString.call) ?

let testDate = new Date("2025-06-07")
let testText = "1 day ago"
let input = { "instant": testDate, "timezone": testDate.getTimezoneOffset() }
const parsedDate = chrono.parseDate(periodText, refDate);

[ted-ks]

To see the Date behaviour in Bigquery

CREATE TEMPORARY FUNCTION test()
RETURNS BOOL
LANGUAGE js
AS
"""
const d = new Date();
return d instanceof Date;
""";
SELECT test();