Question

I have following Jsonstring

  var j = { "name": "John" };
            alert(j.length);

it alerts : undefined, How can i find the length of json Array object??

Thanks

Answer 1

Lets start with the json string:

var jsonString = '{"name":"John"}';

you can easily determine its length:

alert("The string has "+jsonString.length+" characters"); // will alert 15

Then parse it to an object:

var jsonObject = JSON.parse(jsonString);

A JavaScript Object is not an Array and has no length. If you want to know how many properties it has, you will need to count them:

var propertyNames = Object.keys(jsonObject);
alert("There are "+propertyNames.length+" properties in the object"); // will alert 1

If Object.keys, the function to get an Array with the (own) property names from an Object, is not available in your environment (older browsers etc.), you will need to count manually:

var props = 0;
for (var key in jsonObject) {
    // if (j.hasOwnProperty(k))
    /* is only needed when your object would inherit other enumerable
       properties from a prototype object */
        props++;
}
alert("Iterated over "+props+" properties"); // will alert 1