Working with Dates
Dates and times are common in web applications. Learn how to format and manipulate dates reliably.
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📋 Copy Intl.DateTimeFormat & Safe Date Math Snippet
// Modern Intl.DateTimeFormat & Timestamp Calculations
const now = new Date();
// High-Precision Localized Formatting
const formatter = new Intl.DateTimeFormat("en-US", {
dateStyle: "full",
timeStyle: "short",
timeZone: "America/New_York"
});
console.log(formatter.format(now));
// Date Arithmetic via Timestamps
const tomorrow = new Date(now.getTime() + 24 * 60 * 60 * 1000);⚠️ 5 Fatal Traps & JavaScript Pitfalls
Trap #1: 0-Indexed Months Trap
In JavaScript
Date, months are 0-indexed (January is 0, December is 11). Writing new Date(2026, 1, 1) creates February 1st, NOT January 1st!Trap #2: String Date Parsing Ambiguity
Parsing strings like
new Date("05/06/2026") produces May 6 in the US and June 5 in Europe. Always use ISO 8601 strings: "YYYY-MM-DDTHH:mm:ssZ".Trap #3: In-Place Mutation with Date Setters
Calling
date.setDate(date.getDate() + 7) mutates the original Date instance in-place. Clone before modifying: new Date(date.getTime()).Trap #4: Comparing Dates with Loose or Strict Equality
dateA === dateB compares object memory references, returning false even if both dates represent the exact same millisecond. Compare with dateA.getTime() === dateB.getTime().Trap #5: Daylight Saving Time (DST) Arithmetic Offsets
Adding 86,400,000 milliseconds (24 hours) across a DST transition can shift clock times by 1 hour. Use calendar setters or modern Temporal APIs.
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