空的json输出导致错误“在非对象上调用Object.keys”

Question

I received an error Object.keys called on non-object . The offending code is;

numberOfEmployees = Object.keys(employee_data).length;

employee_data is a json object that gets assigned json output data from a web service. This error only happens when the json output is empty [] . If json output is not empty, there is no error. What is wrong with the code?

employee_data becomes undefined when the json output is empty [] .

Answer 1

The error Object.keys called on non-object can only occured when you put non object into it. See below in https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/keys

return function(obj) {
      if (typeof obj !== 'object' && (typeof obj !== 'function' || obj === null)) {
        throw new TypeError('Object.keys called on non-object');
      }

Did you test what is the value of employee_data when it is empty. It should work for [ ] .

But if you have called JSON.stringify on it,than it won't work, See below.

var emptyData = [];
if(typeof emptyData == 'object')
   console.log(Object.keys(emptyData)); // it will print the keys,if there

var emptyData = [];
var emptyJSOn = JSON.stringify(emptyData);
if(typeof emptyJSOn == 'object')
   console.log(emptyJson); //  it won't print because ,it's not an object.

Now i suppose you are trying to pass, the emptyJson to Object.keys() method,which is why you are receiving this error.

For more information on this you can refer MDN docs.