parsing JSON data with java script

Question

I use Google plus API and get this data from it and get an error while parsing this JSON data

and here is the code I use to parse this data and get error as data object is tested and work fine and hold data as it appear in past 2 images

var allIems = data.items;
for (var element in allIems) {
  document.getElementById('datafromapi').innerHTML +=
    (" , published time :" + element.published +
      " , last updated time :" + element.updated +
      ", complete url : " + element.url

    );
  var obj = element.object.attachments;

  document.getElementById('datafromapi').innerHTML +=
    (+"\nattachments of post :\n" +
      " type : " +
      obj[0].objectType +
      " ,displayName of content : " +
      obj[0].displayName +
      " ,content URL  : " +
      obj[0].url +
      " ,content data :" +
      obj[0].image.url +
      " ,content type : " +
      obj[0].image.type +
      " ,content height : " +
      obj[0].image.height +
      " ,content width : " +
      obj[0].image.width +
      "\n\n\n");


}
});

i got that error appear

Uncaught TypeError: Cannot read property 'attachments' of undefined

This error because NOT all element contain the object property. — Mohamed Abbas
– Mohamed Abbas, Commented Jun 23, 2017 at 18:18
the error is on attachments attribute not object and all elements have object attribute — ahmed khattab
– ahmed khattab, Commented Jun 23, 2017 at 18:21
@ahmedkhattab The error says that element.object is undefined. Since it's undefined, it doesn't have any attributes. — Barmar
– Barmar, Commented Jun 23, 2017 at 18:22
@ahmedkhattab he's right, the object attribute is undefined. — user47589
– user47589, Commented Jun 23, 2017 at 18:22
@ahmedkhattab Check your first item in your allIems array. — Mohamed Abbas
– Mohamed Abbas, Commented Jun 23, 2017 at 18:25

Igor · Accepted Answer · 2017-06-23 18:52:54Z

1

element values in

for (var element in allIems) {

are keys of allItems, which in this case are array indices. You have to address the actual array items like this:

var obj = allItems[element].object.attachments;

Your code element.object.attachments; tries to access property object of a number, which does not exist.

Since we know that allItems is an array, you could have written:

for (var i = 0; i < allIems.length; i++) {
  var obj = allItems[i].object.attachments;

edited Jun 23, 2017 at 18:52

answered Jun 23, 2017 at 18:27

Igor

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Comments

Jordankid93 · Accepted Answer · 2017-07-10 03:42:44Z

1

Javascript has a built in JSON parser you can use that takes in a string of the data and returns an object.

let jsonDataAsString = "{\"a\":1,\"b\":2}";

let jsonDataAsObject = JSON.parse(jsonDataAsString);

Then you can traverse through the data as an object, referencing properties using dot-notation

console.log(jsonDataAsObject.a); // 1

To be safe, you should be comparing properties to null before trying to use then

if(jsonDataAsObject.somePropery != null) {
    // the property exists so you can access it here
}

edited Jul 10, 2017 at 3:42

answered Jun 23, 2017 at 18:25

Jordankid93

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2 Comments

scunliffe Over a year ago

You likely want to check if the property is undefined first, as it could be defined and set to null (completely valid)

Jordankid93 Over a year ago

@scunliffe as far as I've ever used it null == undefined so as long as you us != you should be good. Though if you're someone who likes to use === then yes you would need to be more careful with checking before trying to access properties

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