date_testing.ts

function zeroPad(num: number, count: number, radix: number = 10): string {
    if (num < 0) return "-" + zeroPad(-num, count, radix);
    const str = (num | 0).toString(radix);
    if (str.length > count) return str;
    return ("0".repeat(count) + str).substr(-count);
}

function formatDate(date: Date) {
    return zeroPad(date.getFullYear(), 4) + "-" + zeroPad(date.getMonth()+1, 2) + "-" + zeroPad(date.getDate(), 2)
}

const date = "2020-01-29T08:00:00-0700"
const rdate = new Date(Date.parse(date));
const nfilename = `${formatDate(rdate)}`;
console.log("translated date is: ", nfilename);
console.log("month is ", rdate.getMonth());

console output from https://www.typescriptlang.org/play/

translated date is:  2020-01-29
month is  0