addClasses()

import { addClasses } from "@unifast/node";

Signature

function addClasses(rules: Record<string, string>): UnifastPlugin

Parameters

rules

A Record<string, string> where keys are CSS selectors and values are space-separated class names to add to matching elements. Classes are merged with any existing classes on the element.

Supported selectors

Supports a wide subset of CSS Selectors Level 4 including:

• Tag selectors: h1, p, table

• Class selectors: .info, .alert.warning

• ID selectors: #main

• Universal selector: *

• Attribute selectors: [data-type], [href^="https"], [href$=".pdf"], [href*="example"], [class~="bar"], [lang|="en"]

• Combinators: descendant ( ), child (>), adjacent sibling (+), general sibling (~)

• Pseudo-classes: :first-child, :last-child, :nth-child(), :not(), :empty

• Comma-separated selectors: h1, h2, h3

• Compound selectors: div.alert#main[data-type="warning"]

Usage

import { compile, addClasses } from "@unifast/node";

const md = `
# Hello World

Some paragraph text.

| Name | Value |
|------|-------|
| A    | 1     |
`;

const result = compile(md, {
  plugins: [
    addClasses({
      h1: "text-3xl font-bold",
      p: "leading-relaxed",
      table: "border-collapse w-full",
    }),
  ],
});

// <h1 class="text-3xl font-bold">Hello World</h1>
// <p class="leading-relaxed">Some paragraph text.</p>
// <table class="border-collapse w-full">...</table>

Examples

Comma-separated selectors

Apply the same classes to multiple element types:

import { compile, addClasses } from "@unifast/node";

const result = compile(md, {
  plugins: [
    addClasses({
      "h1, h2, h3": "font-bold tracking-tight",
    }),
  ],
});

Complex selectors

Use combinators and pseudo-classes for precise targeting:

import { compile, addClasses } from "@unifast/node";

const result = compile(md, {
  plugins: [
    addClasses({
      "pre > code": "block overflow-x-auto",
      "ul > li:first-child": "mt-0",
      "ul > li:last-child": "mb-0",
      "a[href^=\"https\"]": "external-link",
      "div:not(.alert)": "default-container",
    }),
  ],
});

Tailwind CSS utility classes

A common pattern is using addClasses to apply Tailwind utilities to Markdown-generated HTML:

import { compile, addClasses } from "@unifast/node";

const result = compile(md, {
  plugins: [
    addClasses({
      h1: "text-4xl font-extrabold text-gray-900 mb-8",
      h2: "text-2xl font-bold text-gray-800 mt-12 mb-4",
      h3: "text-xl font-semibold text-gray-700 mt-8 mb-3",
      p: "text-base leading-7 text-gray-600 mb-4",
      a: "text-blue-600 underline hover:text-blue-800",
      blockquote: "border-l-4 border-gray-300 pl-4 italic text-gray-500",
      table: "min-w-full divide-y divide-gray-200",
      "thead th": "px-4 py-2 text-left text-sm font-semibold text-gray-900",
      "tbody td": "px-4 py-2 text-sm text-gray-700",
      "tbody tr:nth-child(2n)": "bg-gray-50",
      img: "rounded-lg shadow-md",
      pre: "rounded-lg overflow-hidden",
      "pre > code": "block p-4 text-sm",
    }),
  ],
});

Attribute selectors

Target elements based on their attributes:

import { compile, addClasses } from "@unifast/node";

const result = compile(md, {
  plugins: [
    addClasses({
      "[href$=\".pdf\"]": "pdf-link",
      "[href^=\"https\"]": "external",
      "[data-type]": "has-type",
    }),
  ],
});