CODEWITHSUNDEEP
javascript
user1050619
user1050619

Reputation: 20856

find Javascript object length

Im trying to find the length of the report_data(object) key using the below code..but for some reasons it yields value 3.

a={report_freq: "daily", report_item_num: 2, report_num: 39, report_data: "{}"}
Object {report_freq: "daily", report_item_num: 2, report_num: 39, report_data: "{}"}
Object.getOwnPropertyNames(a.report_data).length
3

for more clarity I have the image.

enter image description here

Upvotes: 0

Views: 156

Answers (2)

JDB
JDB

Reputation: 25820

a.report_data is a string with three properties:

  • 0, representing the first character ("{").

  • 1, representing the second character ("}").

  • and length, representing the length of the string (2).

It's a little counter-intuitive, if you come from other languages, that 0 and 1 are properties, but in Javascript array elements are properties just like all other properties, and "regular" properties can be accessed using array syntax (aka "bracket notation"):

// "array elements"
a.report_data[0]        === "{";
a.report_data[1]        === "}";
// or...
a.report_data["0"]      === "{";
a.report_data["1"]      === "}";

// "normal" properties
a.report_data.length    === 2;
// or...
a.report_data["length"] === 2;

These are all property names, and, thus, when you ask for an array of property names for your string, you get:

["0", "1", "length"]

Upvotes: 6

jmar777
jmar777

Reputation: 39649

Assuming you want the length of the actual string value, then you simply want to use report_data.length, as demonstrated here:

var a = {
  report_freq: "daily",
  report_item_num: 2,
  report_num: 39,
  report_data: "{}"
};

console.log(a.report_data.length)

Your current code includes this:

Object.getOwnPropertyNames(a.report_data).length

If you look at the docs for Object.getOwnPropertyNames(obj), you'll see the following description:

Object.getOwnPropertyNames() returns an array whose elements are strings corresponding to the enumerable and non-enumerable properties found directly upon obj.

So, in this case, Object.getOwnPropertyNames(a.report_data) returns an array containing the keys found on the string, and there happens to be 3 of them.

Upvotes: 0

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