@kangc/v-md-editor/src/utils/markdown-it-katex.js

A markdown editor built on Vue

// Modified from https://github.com/waylonflinn/markdown-it-katex/blob/master/index.js

/* eslint-disable */
function isValidDelim(state, pos) {
  let prevChar;
  let nextChar;
  const max = state.posMax;
  let can_open = true;
  let can_close = true;

  prevChar = pos > 0 ? state.src.charCodeAt(pos - 1) : -1;
  nextChar = pos + 1 <= max ? state.src.charCodeAt(pos + 1) : -1;

  if (
    prevChar === 0x20 /* " " */ ||
    prevChar === 0x09 /* \t */ ||
    (nextChar >= 0x30 /* "0" */ && nextChar <= 0x39) /* "9" */
  ) {
    can_close = false;
  }
  if (nextChar === 0x20 /* " " */ || nextChar === 0x09 /* \t */) {
    can_open = false;
  }

  return {
    can_open,
    can_close,
  };
}

function math_inline(state, silent) {
  let start;
  let match;
  let token;
  let res;
  let pos;
  let esc_count;

  if (state.src[state.pos] !== '$') {
    return false;
  }

  res = isValidDelim(state, state.pos);
  if (!res.can_open) {
    if (!silent) {
      state.pending += '$';
    }
    state.pos += 1;
    return true;
  }

  start = state.pos + 1;
  match = start;
  while ((match = state.src.indexOf('$', match)) !== -1) {
    pos = match - 1;
    while (state.src[pos] === '\\') {
      pos -= 1;
    }

    if ((match - pos) % 2 == 1) {
      break;
    }
    match += 1;
  }

  if (match === -1) {
    if (!silent) {
      state.pending += '$';
    }
    state.pos = start;
    return true;
  }

  if (match - start === 0) {
    if (!silent) {
      state.pending += '$$';
    }
    state.pos = start + 1;
    return true;
  }

  res = isValidDelim(state, match);
  if (!res.can_close) {
    if (!silent) {
      state.pending += '$';
    }
    state.pos = start;
    return true;
  }

  if (!silent) {
    token = state.push('math_inline', 'math', 0);
    token.markup = '$';
    token.content = state.src.slice(start, match);
  }

  state.pos = match + 1;
  return true;
}

function math_block(state, start, end, silent) {
  let firstLine;
  let lastLine;
  let next;
  let lastPos;
  let found = false;
  let token;
  let pos = state.bMarks[start] + state.tShift[start];
  let max = state.eMarks[start];

  if (pos + 2 > max) {
    return false;
  }
  if (state.src.slice(pos, pos + 2) !== '$$') {
    return false;
  }

  pos += 2;
  firstLine = state.src.slice(pos, max);

  if (silent) {
    return true;
  }
  if (firstLine.trim().slice(-2) === '$$') {
    firstLine = firstLine.trim().slice(0, -2);
    found = true;
  }

  for (next = start; !found; ) {
    next++;

    if (next >= end) {
      break;
    }

    pos = state.bMarks[next] + state.tShift[next];
    max = state.eMarks[next];

    if (pos < max && state.tShift[next] < state.blkIndent) {
      break;
    }

    if (state.src.slice(pos, max).trim().slice(-2) === '$$') {
      lastPos = state.src.slice(0, max).lastIndexOf('$$');
      lastLine = state.src.slice(pos, lastPos);
      found = true;
    }
  }

  state.line = next + 1;

  token = state.push('math_block', 'math', 0);
  token.block = true;
  token.content =
    (firstLine && firstLine.trim() ? firstLine + '\n' : '') +
    state.getLines(start + 1, next, state.tShift[start], true) +
    (lastLine && lastLine.trim() ? lastLine : '');
  token.map = [start, state.line];
  token.markup = '$$';
  return true;
}

module.exports = function math_plugin(md, options) {
  options = options || {};

  const { katex } = options;

  const katexInline = function (latex) {
    options.displayMode = false;
    try {
      return katex.renderToString(latex, options);
    } catch (error) {
      if (options.throwOnError) {
        console.log(error);
      }
      return latex;
    }
  };

  const inlineRenderer = function (tokens, idx) {
    return katexInline(tokens[idx].content);
  };

  const katexBlock = function (latex) {
    options.displayMode = true;
    try {
      return '<p>' + katex.renderToString(latex, options) + '</p>';
    } catch (error) {
      if (options.throwOnError) {
        console.log(error);
      }
      return latex;
    }
  };

  const blockRenderer = function (tokens, idx) {
    return katexBlock(tokens[idx].content) + '\n';
  };

  md.inline.ruler.after('escape', 'math_inline', math_inline);
  md.block.ruler.after('blockquote', 'math_block', math_block, {
    alt: ['paragraph', 'reference', 'blockquote', 'list'],
  });
  md.renderer.rules.math_inline = inlineRenderer;
  md.renderer.rules.math_block = blockRenderer;
};