Date.parse() converts a date string into milliseconds since the Unix epoch. This guide covers syntax, ISO 8601 best practices, validation, time-difference math, and how it compares to new Date(string).
Date.parse(str)
On Date
Best format
Returns NaN
Same ms
Number.isNaN
APIs, forms, and JSON payloads often deliver dates as strings. Before you compare, sort, or subtract them, you need a numeric timestamp. Date.parse() is a static method that performs that conversion in one step.
It returns epoch milliseconds (like Date.now()) or NaN when the string cannot be parsed. For many workflows, new Date(string) is equally fine—but Date.parse() is handy when you only need the number.
Date.parse() MethodDate.parse(dateString) is a static method on the Date constructor. It does not create a Date object; it returns the parsed instant as a number of milliseconds since January 1, 1970 00:00:00 UTC.
For valid ISO 8601 strings, results are consistent across modern browsers and Node.js. Ambiguous formats like 03/04/2025 may parse differently depending on implementation—prefer explicit ISO strings in production.
Date.parse(str) is equivalent to new Date(str).getTime() when the string parses successfully. Use Number.isNaN(Date.parse(str)) to catch bad input.
Date.parse(dateString)dateString — A string representing a date and time (ISO 8601 recommended).NaN if the string cannot be parsed into a valid instant.| Goal | Code |
|---|---|
| Parse ISO string to ms | Date.parse("2026-03-15T12:00:00.000Z") |
| Build Date from string | new Date(Date.parse(str)) or new Date(str) |
| Check valid parse | !Number.isNaN(Date.parse(str)) |
| Elapsed between strings | Date.parse(end) - Date.parse(start) |
| Same as getTime() | new Date(str).getTime() |
| Human UTC output | new Date(ms).toISOString() |
These APIs all involve strings and timestamps but serve different jobs.
str → msStatic parse
Date objObject wrapper
now msCurrent time
Date → strOpposite direction
Open DevTools Console (F12) or use Try-it links. ISO strings ending in Z parse as UTC for predictable results.
Convert an ISO 8601 string into epoch milliseconds.
UTC strings ending in Z are the most portable format.
const iso = "2026-03-15T12:00:00.000Z";
const timestamp = Date.parse(iso);
console.log("Timestamp (ms):", timestamp);The result is a large integer you can subtract, compare, or pass to new Date(ms). Always validate before using user-provided strings.
Date objects, validation, duration math, and API comparison.
Date from a Parsed TimestampTurn the numeric result back into a Date for formatting or getters.
const iso = "2026-03-15T12:00:00.000Z";
const date = new Date(Date.parse(iso));
console.log(date.toISOString()); // "2026-03-15T12:00:00.000Z"new Date(iso) alone works too—use Date.parse when you need the number first or want to validate before constructing a Date.
Failed parses return NaN. Check before storing or displaying.
function isValidDateString(input) {
return !Number.isNaN(Date.parse(input));
}
console.log(isValidDateString("2026-03-15T12:00:00.000Z")); // true
console.log(isValidDateString("not-a-date")); // falseDate.parse never throws on bad input—it returns NaN. Number.isNaN is the reliable check (avoid loose isNaN on strings).
Parse both strings, subtract timestamps, and convert to hours.
const start = Date.parse("2026-03-15T12:00:00.000Z");
const end = Date.parse("2026-03-15T14:30:00.000Z");
const hours = (end - start) / (1000 * 60 * 60);
console.log("Hours between:", hours); // 2.5Subtracting parsed timestamps gives elapsed milliseconds. Divide by the right factor for seconds, minutes, or hours.
Date.parse() and new Date()For valid strings, both paths yield the same epoch milliseconds.
const iso = "2026-03-15T12:00:00.000Z";
const fromParse = Date.parse(iso);
const fromDate = new Date(iso).getTime();
console.log("Date.parse:", fromParse);
console.log("getTime():", fromDate);
console.log("Equal:", fromParse === fromDate);Choose Date.parse when you only need the number; choose new Date when you will call getters or formatters on the result.
Date.parse(deadline) to Date.now().Date.parse() Converts a StringYou pass a date string to the static parse method.
JavaScript interprets the format (ISO is most reliable).
A single UTC instant is identified internally.
Epoch milliseconds on success; NaN if parsing fails.
2026-03-15T12:00:00.000Z) for cross-environment consistency.NaN—validate with Number.isNaN(Date.parse(str)).01/02/2023 may parse differently by engine or locale.Date.parse(str) === new Date(str).getTime() for successful parses.new Date(ms).toISOString() or locale formatters.Date.parse does not throw—always check the return value.Date.parse() has been available since ES1. ISO 8601 strings parse consistently in all modern browsers and Node.js.
Supported everywhere. Stick to ISO 8601 for predictable parsing across Chrome, Firefox, Safari, Edge, and Node.js.
Bottom line: Safe everywhere. Prefer ISO strings and validate with Number.isNaN before using parsed values.
Date.parse() turns date strings into epoch milliseconds for comparison, sorting, and duration math. Use ISO 8601 input, validate with Number.isNaN, and pair with new Date(ms) or toISOString() for object workflows.
Next, learn toDateString() for readable local date labels, or use toISOString() to serialize dates back to UTC strings.
Z or offset)Number.isNaN(Date.parse(input))toISOString() for logsMM/DD/YYYY strings without testsisNaN("foo") for string validationDate.parse()Your foundation for string-to-timestamp conversion in JavaScript.
Date.parse(str)
Best input.
FormatReturn value.
UnitBad input.
ValidateSame ms.
CompareDate.parse("2026-03-15T12:00:00.000Z") and new Date("2026-03-15T12:00:00.000Z").getTime() return the same milliseconds—parse skips creating a Date when you only need the number.
Format parsed timestamps as readable local calendar date strings.
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