AI solution for JavaScript Coding Question on BFE.dev
22. implement JSON.parse()

function parseJSON(jsonString) {
  const index = { value: 0 };
  
  function parseValue() {
    const start = index.value;
    let result;
    
    switch (jsonString[start]) {
      case '{':
        result = parseObject();
        break;
        
      case '[':
        result = parseArray();
        break;
        
      case '\"':
        result = parseString();
        break;
        
      case 't':
        result = parseTrue();
        break;
        
      case 'f':
        result = parseFalse();
        break;
        
      case 'n':
        result = parseNull();
        break;
        
      default:
        result = parseNumber();
        break;
    }
    
    return result;
  }
  
  function parseObject() {
    index.value++;
    const obj = {};
    
    while (jsonString[index.value] !== '}') {
      const key = parseString();
      
      index.value++;
      const value = parseValue();
      
      obj[key] = value;
      
      if (jsonString[index.value] === ',') {
        index.value++;
      }
    }
    
    index.value++;
    return obj;
  }
  
  function parseArray() {
    index.value++;
    const arr = [];
    
    while (jsonString[index.value] !== ']') {
      const value = parseValue();
      
      arr.push(value);
      
      if (jsonString[index.value] === ',') {
        index.value++;
      }
    }
    
    index.value++;
    return arr;
  }
  
  function parseString() {
    const start = index.value + 1;
    let end = start;
    
    while (jsonString[end] !== '\"') {
      if (jsonString[end] === '\\') {
        end++;
      }
      
      end++;
    }
    
    const str = jsonString.slice(start, end);
    index.value += str.length + 1;
    
    return str;
  }
  
  function parseTrue() {
    index.value += 4;
    return true;
  }
  
  function parseFalse() {
    index.value += 5;
    return false;
  }
  
  function parseNull() {
    index.value += 4;
    return null;
  }
  
  function parseNumber() {
    const start = index.value;
    let end = start;
    
    while ('0123456789-+eE.'.includes(jsonString[end])) {
      end++;
    }
    
    const numStr = jsonString.slice(start, end);
    const num = +numStr;
    index.value += numStr.length;
    
    return num;
  }
  
  return parseValue();
}