Difference between parseISO(string) and new Date(string)?

The difference lies in the way they handle parsing of date strings and in their behavior regarding the interpretation of time zones.

• parseISO(string): This function is typically used in libraries like date-fns for parsing ISO 8601 formatted strings into JavaScript Date objects. ISO 8601 format includes the date and time in a standardized format. parseISO specifically expects strings in ISO 8601 format and converts them into Date objects. Importantly, parseISO treats the provided date string as UTC by default. This means it does not consider the local time zone of the system, but instead assumes that the provided string represents a date and time in UTC.

const date = parseISO('2024-03-20T12:00:00'); console.log(date); // Output: 2024-03-20T12:00:00.000Z (UTC time) 

• new Date(string): This is the built-in JavaScript constructor for creating Date objects from date strings. It accepts a wide variety of date formats, not just ISO 8601, which makes it less strict than parseISO. When you provide a string to new Date, it tries to parse the string and create a Date object based on the local time zone of the system where the code is executed. This can lead to inconsistencies and unexpected behavior, especially when dealing with ambiguous or non-standard date formats.

const date = new Date('2024-03-20T12:00:00'); console.log(date); // Output may vary depending on the system's time zone