markdown-it/lib/rules_core/normalize.js

// Normalize input string

'use strict';


var TABS_SCAN_RE = /[\n\t]/g;
var NEWLINES_RE  = /\r[\n\u0085]|[\u2424\u2028\u0085]/g;
var NULL_RE      = /\u0000/g;


module.exports = function inline(state) {
  var str, lineStart, lastTabPos;

  // Normalize newlines
  str = state.src.replace(NEWLINES_RE, '\n');

  // Replace NULL characters
  str = str.replace(NULL_RE, '\uFFFD');

  // Replace tabs with proper number of spaces (1..4)
  if (str.indexOf('\t') >= 0) {
    lineStart = 0;
    lastTabPos = 0;

    str = str.replace(TABS_SCAN_RE, function (match, offset) {
      var result;
      if (str.charCodeAt(offset) === 0x0A) {
        lineStart = offset + 1;
        lastTabPos = 0;
        return match;
      }
      result = '    '.slice((offset - lineStart - lastTabPos) % 4);
      lastTabPos = offset - lineStart + 1;
      return result;
    });
  }

  state.src = str;
};