Marko in March 2026

TL;DR
  • Bound attribute modifiers like value:Number:=quantity
  • "Did you mean" suggestions for unknown tags
  • Full Rolldown support and initial Vite 8 compatibility
  • Better support for apps embedded inside another app

March added a shorthand for the most common two-way binding chore, closed a nearly decade-old request for friendlier tag errors, and moved the Vite integration onto Rolldown. Around those were steady gains in output size, concise-mode whitespace handling, and Class-to-Tags interop.

Bound Attributes

Two-way bindings often need to normalize a value before storing it. A modifier placed on a bound attribute now does this inline: the identifier after the attribute name processes every value passed to the implicit change handler.

<let/quantity=1>
<input type="number" value:Number:=quantity>
<p>Subtotal: ${(quantity * 4.99).toFixed(2)}</p>
let/quantity=1
input type="number" value:Number:=quantity
p -- Subtotal: ${(quantity * 4.99).toFixed(2)}

Here value:Number:=quantity binds the input and coerces each change through Number before assigning it, replacing a longhand change handler that would otherwise be written out by hand. This is especially convenient when binding to a member expression, where the equivalent handler is verbose. The modifier must be an identifier, so more involved normalization can point at a local static function of the same name.

Editor support shipped alongside the runtime, so the shorthand formats and type-checks correctly (marko#3130, language-server#468). A related fix made bound attributes with an as cast parse correctly instead of erroring (language-server#465, marko#3110).

Clearer Errors

Continuing the recent push to catch mistakes earlier, the compiler now suggests a correction when it meets an unknown tag. A misspelled or unrecognized component name is met with the closest known tag as a suggestion rather than a bare failure, closing a request that had been open for nearly ten years (marko#3114). Invalid attribute names and malformed bind refinement shorthands now produce messages as well, so more authoring mistakes surface at compile time (marko#3133).

Rolldown

The Vite integration gained full Rolldown support, replacing the previous esbuild-based plugin with a dedicated Rolldown plugin (vite#251). Vite 8 is now accepted as a peer dependency, with the remaining esbuild interop to be removed as the plugin settles onto Rolldown (vite#246). Dev-mode dependency scanning was reworked to pre-scan entry templates with htmljs-parser, resolve their tags through the taglib, and register the results in a single pass rather than several (vite#253).

Embedded Apps

Embedding a Marko app inside another page, such as a widget mounted into an existing document, works more smoothly. When a template is detected not to render html, head, or body, Marko now generates a unique $global.renderId automatically, and it cleans up scopes when the embedded DOM is removed (marko#3124).

Improvements

Beyond the headlines, improvements trimmed server output and expanded type coverage.

Performance

Server output got smaller. Duplicate section serialization guards are now emitted once instead of repeatedly (marko#3141). The list reconciliation code was rewritten with its logic inlined for a smaller bundle and additional fast paths for the common case where no items move between renders (marko#3112).

Type Definitions

Native attribute typings expanded, adding webkitdirectory on <input>, media on <meta>, and refined <button> attributes (marko#3121, marko#3137, marko#3138).

Marko Run

Marko Run's file-based routing gained an interactive REPL at marko.run/repl that visualizes how a set of route files maps to matched routes (marko.run#1).

Fixes

Correctness work concentrated on concise-mode whitespace and the Class API interop layer.

Concise Syntax

Several concise-mode whitespace regressions were corrected. Newlines between nodes inside a concise HTML block are preserved again rather than collapsed, and trailing whitespace in those blocks is handled correctly (htmljs-parser#216, htmljs-parser#218). The Tags API <style> translation was updated for the parser's revised text nodes, and the compiler no longer inserts a stray space between adjacent text and placeholders in a tag body (marko#3108, marko#3129).

Interop

Mixing the Class API and Tags API grew more reliable when legacy renderer APIs are involved, with dynamic tags routing correctly through the compatibility layer (marko#3145). A production-mode ordering bug in return-tag analysis was fixed, so intersecting state resolves in the correct order (marko#3135). The @marko/express middleware was updated for Marko 6 (express#12).

In Brief

  • Rendering no longer throws an uninitialized error when input is absent (marko#3125).
  • The compiler avoids loading Babel configuration when Babel is not installed (marko#3118, marko#3119).

Full details for every change are in the release notes of each package on GitHub.

Further Reading

Contributors

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