JsonParser

parser.js

function JsonParser() {}

JsonParser.prototype.parse = function(inputStr) {
  let trimmed = inputStr.replace(/ /g, '')
  if (isArray(trimmed)) {
    return parseArray(trimmed)
  } else if (isObject(trimmed)) {
    return parseObj(trimmed)
  }
}

function parseObj(str) {
  let result = {};
  let beginIndex = 0;
  str = str.slice(1, str.lastIndexOf('}'))

  while (beginIndex < str.length) {
    let sepIndex = str.indexOf(':', beginIndex)
    let key = str.slice(beginIndex, sepIndex).replace(/\"/g, '')
    let value
    let next = str.charAt(sepIndex + 1)

    if (next === '{' || next === '[') {
      let collection = collectJSON(str, sepIndex + 1)
      result[key] = new JsonParser().parse(collection.result)
      beginIndex = collection.index + 1
    } else {
      let endIndex = str.indexOf(',', sepIndex) !== -1
        ? str.indexOf(',', sepIndex)
        : str.length

      value = str.slice((sepIndex + 1), endIndex)
      result[key] = parsePrimitive(value)
      beginIndex = endIndex + 1
    }
  }

  return result;
}

function parseArray(str) {
  let result = [];
  let beginIndex = 0;
  str = str.slice(1, str.lastIndexOf(']'));

  while (beginIndex < str.length) {
    let sepIndex = str.indexOf(',', beginIndex) !== -1
      ? str.indexOf(',', beginIndex)
      : str.length
    let item = str.slice(beginIndex, sepIndex)

    if (item.indexOf('{') !== -1 || item.indexOf('[') !== -1) {
      let collection = collectJSON(str, beginIndex)
      result.push(new JsonParser().parse(collection.result))
      beginIndex = collection.index + 1
    } else {
      result.push(parsePrimitive(item))
      beginIndex = sepIndex + 1
    }
  }

  return result;
}

function parsePrimitive(str) {
  if (str.indexOf('"') !== -1) return String(str)
  else if (str.indexOf('.') !== -1) return parseFloat(str)
  else return parseInt(str)
}

function collectJSON(str, startIndex) {
  let counter = 0
  let index = startIndex
  let result = ''
  do {
    let char = str.charAt(index)
    if (char === '{' || char === '[') counter++
    else if (char === '}' || char === ']') counter--
    result += char
    index++
  } while (counter !== 0)
  return {result: result, index: index}
}

function isArray(str) {
  return str.length !== 0 && str[0] === '['
}

function isObject(str) {
  return str.length !== 0 && str[0] === '{'
}

function main() {
  var jsonParser = new JsonParser();

  console.log("First Step");
  var result = jsonParser.parse(" [ 10, 20, 30.1 ] ");
  for (var i = 0; i < result.length; i++) {
    console.log(result[i]);
  }

  console.log("\nSecond Step");
  result = jsonParser.parse(" [ 10 , 20, \"hello\", 30.1 ] ");
  for (var i = 0; i < result.length; i++) {
    console.log(result[i]);
  }

  result = jsonParser.parse('{ \
            "hello": "world",\
            "key1": 20,\
            "key2": 20.3,\
            "foo": "bar" }');
  console.log("\nThird Step");
  for (var key in result) {
    if (result.hasOwnProperty(key)) {
      console.log(key, result[key]);
    }
  }

  result = jsonParser.parse('{\
            "hello": "world",\
            "key1": 20,\
            "key2": {"b": 20.3},\
            "foo": {\
                "hello1": "world1",\
                "key3": [\
                  [200],\
                  300]\
            } }');
  console.log("\nFourth Step");
  for (var key in result) {
    if (result.hasOwnProperty(key)) {
      if (result[key] instanceof Object) {
        for (var key2 in result[key]) {
          console.log(key2, result[key][key2]);
        }
      } else {
        console.log(key, result[key]);
      }
    }
  }
  console.log(result.foo.key3)
}

main();

// Please do not modify the following line.
var module = module || {};
module.exports = JsonParser;