使用递归下降解析一个JSON字符串

使用js解析JSON字符串

	// 记录解析的索引
	var index = 0;
	// 解析入口函数
	function parseItem(str) {
	  let re = null;
	  if (str[index] == "," || str[index] == ":") {
	    index++;
	  }
	  if (str[index] == "[") {
	    re = parseArray(str);
	  } else if (str[index] == "{") {
	    re = parseObject(str);
	  } else {
	    re = parseValue(str);
	  }
	  return re;
	}
	
	// 解析对象
	function parseObject(str) {
	  index++;
	  let re = {};
	  while (index < str.length) {
	    if (str[index] == "}") {
	      index++;
	      break;
	    } else {
	      re[parseItem(str)] = parseItem(str);
	    }
	  }
	  return re;
	}
	
	// 解析数组
	function parseArray(str) {
	  index++;
	  let re = [];
	  while (index < str.length) {
	    if (str[index] == "]") {
	      index++;
	      break;
	    } else {
	      re.push(parseItem(str));
	    }
	  }
	  return re;
	}
	
	// 解析数字
	function parseNumber(target) {
	  if (!isNaN(target)) {
	    return Number(target);
	  } else {
	    return target;
	  }
	}
	// 解析布尔值
	function parseBoolean(target) {
	  if (target == "true") {
	    return true;
	  }
	  if (target == "false") {
	    return false;
	  }
	  return target;
	}
	// 解析null
	function parseNull(target) {
	  if (target === "null") {
	    return null;
	  }
	  return target;
	}
	// 解析非对象的值
	function parseValue(str) {
	  let re = "";
	  while (index < str.length) {
	    if (jugde(str[index])) {
	      break;
	    } else {
	      re += str[index] == '"' ? "" : str[index];
          index++;
	    }
	  }
	  return parseTarget(re);
	}
	
	function parseTarget(target) {
	  target = parseNumber(target);
	  target = parseNull(target);
	  target = parseBoolean(target);
	  return target;
	}
	
	function jugde(char) {
	  return (
	    char == "," ||
	    char == "[" ||
	    char == "{" ||
	    char == "]" ||
	    char == "}" ||
	    char == ":"
	  );
	}
	// 测试
	var jsonText ='[111,222e100,{"a":3},{"b":true,"c":"fooobar","d":[1,false,[null,4,{"x":1,"y":2}]]}]';