JsonParser coding exercise solution. 50 minutes to complete the exercise. Room for improvement? Definitely!

main.js

function JsonParser() {}

function convert(token, type) {
  if (type === "number") {
    return Number(token);
  } else if (type === "string") {
    return String(token);
  }
}

function tokenize(str) {
  var tokens = [];
  var token = "";
  var type = "";
  str.split("").forEach(function (char) {
    if (char === "[" || char === "{") {
      tokens.push(char);
      token = "";
      type = "";
    } else if (char === "," || char === ":") {
      tokens.push(convert(token, type));
      tokens.push(char);
      token = "";
      type = "";
    } else if (char === "]" || char === "}") {
      if (token) {
        tokens.push(convert(token, type));
      }
      tokens.push(char);
      token = "";
      type = "";
    } else if (/\d/.test(char) || char === ".") {
      if (!token) {
        type = "number";
      }
      token += char;
    } else if (char === "\"") {
      if (!token) {
        type = "string";
      }
    } else {
      token += char;
    }
  })
  return tokens;
}

function buildArray(tokens) {
  var result = [];
  while (tokens.length) {
    var token = tokens.shift();
    if (token === "]") {
      return result;
    } else if (token != ",") {
      result.push(token);
    }
  }
}

function buildObject(tokens) {
  var result = {};
  var key = "";
  var value = "";
  while (tokens.length) {
    var token = tokens.shift();
    if (token === "}" && !key) {
      return result;
    } else if (token === "}" && key) {
      result[key] = value;
      return result;
    } else if (token === "," && key) {
      result[key] = value;
      key = "";
      value = "";
    } else if (!key) {
      key = token;
    } else if (token !== "" && key) {
      tokens.unshift(token);
      value = build(tokens);
    }
  }
}

function build(tokens) {
  var token = tokens.shift()
  if (token === "[") {
    return buildArray(tokens);
  } else if (token === "{") {
    return buildObject(tokens);
  } else {
    return token;
  }
}

JsonParser.prototype.parse = function(inputStr) {
  var cleanStr = inputStr
    .split(" ")
    .filter(item => !!item)
    .join("");
  return build(tokenize(cleanStr));
}

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": 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]);
      }
    }
  }
}

main();

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