Lodash _.isDate() method

Beginner
⏱️ 6 min read
📚 Updated: May 2026
🎯 3 Code examples
🚀 3 Try-it labs
Lodash

What you’ll learn

  • How _.isDate(value) detects Date instances via the built-in object tag.
  • Why numeric timestamps and ISO strings fail until you construct Date objects.
  • That “Invalid Date” values remain Dates—use getTime() when validating.
  • When lodash complements plain typeof / instanceof checks in pipelines.

Prerequisites

Comfort with JavaScript Date construction and parsing JSON timestamps into real dates.

  • You understand typeof new Date() is "object", not "date".
  • You can run Try-it labs with the lodash CDN snippet.

Overview

Use _.isDate inside lodash-heavy services when unknown payloads might carry Dates, epoch numbers, or ISO strings—and you want a single helper that mirrors the official Lang semantics.

Typed objects

Positive only for values tagged as Dates, not bare strings or numbers.

Parse first

Normalize API strings with new Date(...) before lodash sees them.

Invalid ≠ absent

Invalid Date objects still pass—validate wall-clock meaning separately.

Syntax

javascript
_.isDate(value)
  • value: any value to test.
  • Returns: true if value is classified as a Date object; otherwise false.
1

Constructed Date instances

Fresh Dates from the constructor—whether “now” or parsed strings—are recognized immediately.

javascript
import isDate from "lodash/isDate";

isDate(new Date());              // true

isDate(new Date("2024-06-01")); // true
Try it Yourself
2

Strings, timestamps, and plain objects

Serialization layers often expose ISO strings or epoch milliseconds—lodash keeps these distinct until you parse.

javascript
import isDate from "lodash/isDate";

isDate("2024-06-01");           // false

isDate(1717200000000);          // false

isDate({ year: 2024, month: 6 }); // false
Try it Yourself
3

Invalid Date objects still match

Parsing failures yield Date objects whose clock is NaN—_.isDate stays true; gate business logic with getTime().

javascript
import isDate from "lodash/isDate";

var bad = new Date("totally-not-a-date");

isDate(bad);                     // true

Number.isNaN(bad.getTime());    // true
Try it Yourself

📋 _.isDate vs related checks

APIMatches
_.isDate(x)Built-in Date instances (including Invalid Date objects).
_.isString(x)Unicode strings—often how APIs ship timestamps before parsing.
_.isNumber(x)Numeric primitives such as epoch milliseconds.
Number.isFinite(x.getTime())Calendar validity after you already hold a Date.

Pitfalls to avoid

JSON

ISO strings stay strings

JSON.parse does not revive Dates automatically—map fields through new Date when needed.

typeof

typeof cannot spot Dates

Both Dates and plain objects read as "object"; lodash isolates the Date tag without manual string checks.

Validity

Type ≠ meaningful instant

Combine _.isDate with getTime(), range checks, or timezone-aware utilities for UX-critical scheduling.

❓ FAQ

No. Strings stay strings until you parse them—pass the result of new Date(...) or another parser if you need to detect Date objects.
No. Invalid Date objects still satisfy _.isDate. Combine it with Number.isNaN(d.getTime()) or your validation library when you need a real instant.
Both usually agree for ordinary objects. Lodash uses tag detection, which can behave more consistently across realms than instanceof alone in advanced embedding scenarios.
No. Millisecond counts are numbers—convert explicitly with new Date(ms) before checking if you treat both shapes in one API.

Summary

  • Purpose: classify values as Date objects inside lodash pipelines.
  • Remember: strings and numbers require parsing; Invalid Date still passes _.isDate.
  • Next: explore more on Lodash _.isElement().
Did you know?

_.isDate relies on the internal [object Date] tag. An “Invalid Date” produced by new Date("???") is still a Date object, so lodash returns true—validate with Number.isNaN(value.getTime()) when you care about real instants.

About the author

Mari Selvan M P
Mari Selvan M P 🔗

Developer, cloud engineer, and technical writer

  • Experience 12 years building web and cloud systems
  • Focus Full Stack Development, AWS, and Developer Education

I write practical tutorials so students and working developers can learn by doing—from databases and APIs to deployment on AWS.

AWS Certified Developer – Associate (Credly)

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