http.etag.weakEqual

Weak ETag comparison: compares opaque-tag values ignoring the weak/strong flag per RFC 9110 §8.8.3.2.

Signature

function weakEqual(a: ETag, b: ETag): boolean

Type Definitions:

• ETag — interface

Problem

RFC 9110 defines two ETag comparison functions with different semantics. Weak comparison ignores the W/ flag and is used for If-None-Match (304 Not Modified). Implementing the wrong comparison function leads to incorrect cache behavior.

How It Works

Compares a.value === b.value, ignoring the weak flag on both operands.

Boundaries

• Ignores the weak flag — W/"abc" equals "abc".
• For strong comparison (If-Match), use strongEqual instead.

Replaces

Common boilerplate this function replaces:

a.value === b.value

Examples

http.etag.weakEqual({ weak: true, value: "a" }, { weak: false, value: "a" });  // true
http.etag.weakEqual({ weak: true, value: "a" }, { weak: true, value: "b" });  // false

Standards

• RFC 9110 §8.8.3.2 — Weak Comparison

Caveats

• Use weakEqual for If-None-Match (304 Not Modified) scenarios.
• Use strongEqual for If-Match scenarios where byte-level identity is required.

FAQ

What is weak ETag comparison?

Weak comparison ignores the W/ flag and compares only the opaque-tag values. Used for If-None-Match / 304 Not Modified.

When should I use weak vs strong ETag comparison?

Use weakEqual for If-None-Match (caching). Use strongEqual for If-Match (range requests, conditional writes).

Does weakEqual care about the W/ prefix?

No. weakEqual({ weak: true, value: 'a' }, { weak: false, value: 'a' }) returns true.

Is weakEqual the correct comparison for 304 Not Modified?

Yes. RFC 9110 §13.1.2 specifies weak comparison for If-None-Match evaluation.

What is the difference between weakEqual and strongEqual?

weakEqual ignores the W/ flag. strongEqual requires both ETags to be strong (weak: false) and have matching values.