Cant read Javascript object from Ajax request

Question

I have the following object that is structured as below in chrome network-> preview window:

n_days_orders: 
    index: ["Sun, 21 Oct 2018", "Mon, ...
    last_n: 7
    quantity: [0, 0, 0, 0, 0, 0, 0]

I am using the following to check if is a JSON object and if so parse it.

after How can I check if a value is a json object?

function isJSON (something) {
  if (typeof something !== 'string') {
    something = JSON.stringify(something)
  }
  try {
    JSON.parse(something)
    return true
  } catch (e) {
    return false
  }
}

if (isJSON(data.n_days_orders)) {
    try {
        daysOrders = JSON.parse(data.n_days_orders)
    } catch (e) {
        console.log(e.message)
        //the line below is printed
        >>Unexpected token o in JSON at position 1
    }
}

How can I get the value in the object without throwing an error?

What is the problem? you did not say what exactly is it you are after and why the current way doesn't work for you — vsync, Oct 28 '18 at 14:13
You need to parse `data` first. A string will not have properties like `n_days_orders` until you convert it to an object — charlietfl, Oct 28 '18 at 14:17
That error usually means that the data is already an object, not a JSON string, so there's no need to call `JSON.parse` on it. — Daniel Beck, Oct 28 '18 at 14:17
[There is no such thing as a "JSON Object"](https://stackoverflow.com/questions/2904131/what-is-the-difference-between-json-and-object-literal-notation). `isJSON({})` evaluates to true but `{}` is not JSON at all. — str, Oct 28 '18 at 14:19
(Remember JSON is a *string* that can be converted into an object; it is not the object itself. Assuming you're getting this data via a jQuery AJAX request, it's probably already done the conversion for you before this code runs; it does this automatically based on the response MIME type or the dataType declared in the call.) — Daniel Beck, Oct 28 '18 at 14:30

score 1 · Accepted Answer · answered Oct 28 '18 at 15:32

Try isJSON as a parser to detect and try parse the value or throw an error. A way to access obj property without having problems with its existence on a reference is by the index value

let t = data.n_days_orders //will raise an exception if the field does not exist;
let tmp = data['n_days_orders'] //will allow you the cast and return an undefined value

A proper way to check a string if it is a valid JSON is to try to parse it and handle an exception. js typeof comparison will return 'object'.

If you are willing to create a prototype or a checker of a JSON format described by a model, a way is to check its fields in a loop and check their existence but this will cost you an O(props) notation for each object so care for delays.

function checkMyModel(model , prototypemodel){
    let props = Object.keys(prototypemodel);
    let notexist = props.filter((p)=>{
        return (model[p] === undefined );
    })
    console.log(notexist);
    return notexist.length > 0 ? false : true;
}
var proto = {id: null, name:null , value:null , z : null }
var m1 = {id: 1, name:'john' , z : null }
var m2 = {id: 1, name:'john1' ,value:'iam a value2'}
var m3 = {id: 1, name:'john2' ,value:'iam a value3' , z : 34 }

console.log(checkMyModel(m1,proto)); //false missing value
console.log(checkMyModel(m2,proto)); //false missing z

But I suppose you want to check only if the property exists

function isJSON (something) {
  try {
      return(typeof something !== 'object') ? JSON.parse(something) : something;
  } catch (e){ console.warn(e);throw e; }
}
function getDayOrdes (value){
  try {
        let obj = isJSON(value);
        let t= obj['n_days_orders'] ;
        return  (t !== null && t !== undefined) ? t : [];
  } catch (e) { return e.message; }
}

var obj1 = { id : 'order1' , value : '111$'}, obj2 = { id : 'order2' , value : '222$'};
var json1 = { id: '' , n_days_orders: [obj1 , obj2]};
var json2 = JSON.stringify(json1) ,json3 = { id: 1 , values: [obj1 , obj2]};

console.log(getDayOrdes(json1)); //returns obj
console.log(getDayOrdes(json2 + 'zasaza')); //throws json parse error
console.log(getDayOrdes(json2)); //returns obj
console.log(getDayOrdes(json3)); //undefined n_days_orders does not exist

Cant read Javascript object from Ajax request

1 Answers1