eslint-plugin-htm.js

module.exports = {
  create(context) {
    return {
      TaggedTemplateExpression(node) {
        if (!isIdentifier(node.tag, 'html')) return;
        
        const END_QUOTE = {
          `'`: /^[^']*'/g,
          `"`: /^[^"]*"/g
        }
        const matchers = [
          ['text', /[^<>"]*/, ['<', 'expression']],
          ['<', /^</g, ['tag name', 'expression', '/']],
          ['>', /^>/g],
          ['/', /^\//g, ['tag name', 'expression']],
          ['self-closing', /^\s*\/>/g, ['text']],
          ['tag name', /[a-z][a-z0-9-]*/gi],
          ['expression', /$/g, [advance]],
          ['attribute', /^\s+[a-z0-9_-$.]+/gi, ['attribute', 'self-closing']],
          ['attribute', /^\s+[a-z0-9_-$.]+=/gi, ['attribute value']],
          ['attribute value', /^(?:(['"])[^\1]*|[^\s'"]*)/gi, ['string', 'expression']],
          ['end attribute', ([quote]) => END_QUOTE[quote] || /^/g, ['attribute', 'self-closing']],
        ];
        const m = matches.reduce((m, arr) => m.set(arr[0], [].concat(m.get(arr[0]), arr]), new Map());
        let str;
        let i = 0;

        function advance() {
          str = node.quasi.quasis[i++];
        }
        function next(...matches) {
          for (let i=0; i<matches.length; i++) {
            let matcher = m.get(matches[i]);
            if (!Array.isArray(matcher)) matcher = [matcher];
            for (let j=0; j<matcher.length; j++) {
              let [name, reg] = matches[i];
              if (typeof reg === 'function') reg = reg(match);
              reg.lastIndex = index;
              const result = reg.exec(str);
              if (result) {
                index = reg.lastIndex;
                type = name;
                match = result;
                current = matches[i];
                return result;
              }
            }
          }
          throw 'Expected one of: ' + matches.map(m => m[0]);
        }

        let index = 0;
        let current;
        let type;
        let match;

        advance();
        next('text');

        while (str) {
          next(current[2]);
        }
        
        return true;
      }
    };
  }
};

const is = (node, type) => node && node.type === type;
const isIdentifier = (node, name) => is(node, 'Identifier') && node.name === name;