rapid-xml-to-json/index.ts

Fast, dependency-free XML-parser for parsing XML structures into JSON. Optimised for speed and low memory usage.

export function xmlToJson(xml: string) {
  const o: any = {};
  let cur = o;
  let curName = ''
  let curContentList: [number,number][] = [];
  let hasContent = false;
  for (let i = 0; i < xml.length; i++) {
    let curChar = xml[i];
    if (curChar === '<') { // Inside an opening or closing tag
      if (xml[i+1] === '/') { // Inside a closing tag
        cur = cur.__parent;
        if (hasContent) { // Insert content instead of current object
          if (cur[curName] instanceof Array) {
            const lastIdx = cur[curName].length-1;

            cur[curName][lastIdx]['#text'] = ''
            for (let i = 0; i < curContentList.length; i++) {
              let curContent = curContentList[i];
              cur[curName][lastIdx]['#text'] += xml.slice(curContent[0], curContent[1]);
            }
          } else {
            cur[curName]['#text'] = '';            
            for (let i = 0; i < curContentList.length; i++) {
              let curContent = curContentList[i];
              cur[curName]['#text'] += xml.slice(curContent[0], curContent[1]);
            }
          }
        }
        while(xml[i] !== '>') {
          i++;
        }
        curName = '';
      } else if (xml[i+1] === '?' || xml[i+1] === '!') { // Ignore processing instructions, stylesheets, DTD validation, 
        if (xml[i+1] === '!') {
          // Handle declarations
          // TODO: Create skipUntil utility function
          if (xml.startsWith('<!DOCTYPE', i)) { // Doctype
            i+=9;
            while(xml[i] !== '>') {
              i++
            }
          } else if (xml.startsWith('<!--', i)) { // Comment
            i+= 4;
            while(!xml.startsWith('-->', i)) {
              i++;
            }
            i+= 2;
          } else if (xml.startsWith('<![CDATA[', i)) { // Handle CDATA
            i+= 9;
            let contentFrom = i;
            while(!xml.startsWith(']]>', i)) {
              i++;
            }
            let contentTo = i;
            curContentList.push([contentFrom, contentTo]);
            i+=2;
            hasContent = true;
            continue; // Skip hasContent = false 
          }
        } else {
          // Ignore processing instructions and stylesheets
          while(xml[i] !== '>') {
            i++;
          }
        }
        
      } else { // Opening
        // Handle next
        i++; // Move to first char
        let name = ''; // Create a name
        while(xml[i] !== ' ' && xml[i] !== '>' && xml[i] !== '/') { // Go until attributes or closing. TODO: Handle XML attributes
          name += xml[i];
          i++
        }
        let isSelfClosing = false;
        let attrs: [number,number,number,number][] = []
        while(xml[i] !== '>') { // Go until closing tag
          i++;
          if (xml[i] !== ' ' && xml[i] !== '\n' && xml[i] !== '>' && xml[i] !== '/') {
            const attrNameStart = i;
            let attrNameEnd = -1;
            while(xml[i] !== '=') {
              i++;
            }
            attrNameEnd = i;
            i+=2; // Skip ="
            let attrValueStart = i;
            while(xml[i] !== '"' || xml[i-1] === '\\') {
              i++
            }
            attrs.push([attrNameStart, attrNameEnd, attrValueStart, i]);
          }
        }
        if (xml[i-1] === '/') {
          isSelfClosing = true;
        }
        if (cur[name]) { // Already defined, create an array or add to existing array
          if (!(cur[name] instanceof Array)) {
            cur[name] = [cur[name]];
          }
          const next: any = {}
          cur[name].push(next);
          next.__parent = cur;
          if (!isSelfClosing) {
            cur = next;
            curName = name;
          }
          
        } else { // Not defined yet. Create new property on json object
          cur[name] = {};
          cur[name].__parent = cur;
          if (!isSelfClosing) {
            cur = cur[name];
            curName = name;
          }
        }
        if (attrs.length) {
          if (isSelfClosing) { // If it's self-closing with attributes, hop down into it
            if (cur[name] instanceof Array) {
              cur = cur[name][cur[name].length-1];
            } else {
              cur = cur[name];
            }
          }
          cur['$attrs'] = {}
          for (let i = 0; i < attrs.length; i++) {
            cur['$attrs'][xml.slice(attrs[i][0], attrs[i][1])] = xml.slice(attrs[i][2], attrs[i][3]);
          }
          if (isSelfClosing) { // And hop back up
            cur = cur.__parent;
          }
        }
      }
      hasContent = false;
      curContentList = [];
    } else if (curName) { // Inside curName
      let contentFrom = i; // TODO: Handle mixed content
      while(xml[i] !== '<') {
        if(!hasContent && (xml[i] !== ' ' && xml[i] !== '\n')) {
          hasContent = true;
        }
        i++
      }
      let contentTo = i;
      i--
      curContentList.push([contentFrom, contentTo]) // TODO: Trim spaces
    }
  }
  return o;
}