获取对象内部数组的长度

Question

I have a JavaScript object which includes an array. I created a new key, length , which is supposed to store the value of the length of the fields array.

$(document).ready(function() {
var data = {
    "label": "Information",
    "fields": [
        {
            "name": "name",
            "label": "Team Name",
            "type": "string",
            "config": {}
        }
    ],
    "length": fields.length     // Need help with this line
};
$("button").click(function() {
    alert(data.length);
});
});

http://jsfiddle.net/kvtywmtm/

In my fiddle, nothing gets alerted, although it should alert 1, since there is 1 record in the fields array.

Any ideas?

Edit

I know you can get the length OUTSIDE of the object by creating a new variable

var length = data.fields.length;

However, I need the length to be inside of the object.

Answer 1

You can use a getter

 $(document).ready(function() { var data = { "label": "Information", "fields": [{ "name": "name", "label": "Team Name", "type": "string", "config": {} }], get length() { return this.fields.length } }; $("button").click(function() { console.log(data.length); }); }); 

 <script src="https://ajax.googleapis.com/ajax/libs/jquery/1.10.0/jquery.min.js"></script> <button>Click Here</button> 

Answer 2

var data = {
    "label": "Information",
    "fields": [
        {
            "name": "name",
            "label": "Team Name",
            "type": "string",
            "config": {}
        }
    ],
};
data.length = fields.length;

This won't auto-update the length field, but it doesn't seem as if you need it to.

Answer 3

Try this JSFiddle

I don't know what length you need in the alert, but if you need the object data properties length you need the following. Also, to pass fields length you need to add it after declare the array:

JS:

$(document).ready(function() {
    var data = {
        "label": "Information",
        "fields": [
            {
                "name": "name",
                "label": "Team Name",
                "type": "string",
                "config": {}
            }
        ]
    };

    data.length = data.fields.length

    $("button").click(function() {
        alert(Object.keys(data).length);
    });
});