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A stricter, signals driven, JSX based library.


This library includes, in about 3.5Kb, logic to parse a specialized form of JSX and through signals, with effects automatically enabled through components.

The goal of this library is:

  • explore if a better instrumented JSX can actually help performance and memory consumption
  • avoid the need of vDOM, still diffing when necessary through arrays in interpolations
  • create once and map on the fly (JIT) templates for both nodes, fragments, and components
  • fine-tune operations per each interpolation, such as spread properties VS known static properties, conditional holes or signals and, last but not least, arrays of items

Current JSX Interpolations Rules

Following the current set of stricter rules around JSX usage and how to avoid/prevent issues:

  • a Component can not return conditional content: a fragment is fine, and so is any other kind of node with interpolations in it, but return condition ? <a /> : <b /> within a component is not supported, as that is suited for an interpolation hole instead, or a new render, but not really as a Component that returned arbitrary content. Use interpolations for that, and consider components as Custom Elements with a well defined tag wrapper.
  • if an interpolation contains a primitive value (e.g. a string, a number, a boolean or undefined) or a signal which value is primitive, every future update of such interpolation will expect a primitive value or signal carrying a primitive value. Conditional primitives values or signals are fine, but {condition ? "string" : <Component />} is not supported.
  • if a signal is used as interpolation and its value is not primiteve, every future update of such interpolation will expect a signal. Conditional signals are fine, but {condition ? signal : (<Component /> || "string")} is not supported.
  • if an interpolation contains an array of items, every future update of such interpolation will expect a signal. Conditional arrays are fine, but {condition ? [..items] : (<Component /> || "string")} is not supported.


Given the following counter.jsx file:

/** @jsx C *//** @jsxFrag F *//** @jsxInterpolation I */

import {
  createElement as C,
  Fragment as F,
  interpolation as I
} from 'udomsay';

const clicks = signal(0);

function Counter() {
  return (
      <button onclick={() => { clicks.value--; }}>-</button>
      <button onclick={() => { clicks.value++; }}>+</button>

render(<Counter />, document.body);

Providing the following babel.config.json transformer:

  "plugins": [

The result can be tested in CodePen.io.


  • run some benchmark and fine-tune performance, specially around arrays
  • fix all benchmark gotchas!
  • add some TSDoc here and there, at least for the exported API
  • do some code cleanup once previous points are done, trying to shrink further the final brotli and minified size


View Github