Converting JSONobj to Obj not working?

I'm attempting to convert a JSON object to a "normal" object using the following...

        var slaobj = eval('('+s+')');

开发者_如何学Pythons being the JSON. however, it doesnt seem to work (It's `.length' is coming back as undefined). What am I doing wrong?

It's `.length' is coming back as undefined

It won't necessarily have a length property, unless it's an array or some other object that has one. For example:

var json = '{"foo": "Value of foo"}';
var obj = eval('(' + json + ')');
alert(obj.foo); // alerts "value of foo"
alert(obj.length); // alerts "undefined", there's no `length` in `obj`

Live example

Off-topic: Using eval to deserialize JSON text can be a security problem, unless you can unambiguously trust the source of the JSON text (for instance, it's your own server and you're connecting via SSL), because eval doesn't parse JSON, it parses and runs JavaScript code. (Adding the parentheses doesn't really help.) You can get alternatives to using eval from Douglas Crockford's Github page (he's the inventor of JSON). Last I checked, there are three alternatives there, two of which don't use eval at all; see the README at the bottom of the page for details.

Objects don't all have ".length" properties. An object literal like:

{ 'foo': 100, 'bar': 'Abraham Lincoln' }

describes an object that has no ".length" property.

JavaScript Array objects have ".length" properties because of the way the language runtime works. But a plain object in JavaScript only has such a property if you put it there.

How are you retrieving the object?

I would say there has to be something else wrong - are you sure the 's' JSON object was returned correctly? JSON.org

To convert a JSON text into an object, you can use the eval() function. eval() invokes the JavaScript compiler. Since JSON is a proper subset of JavaScript, the compiler will correctly parse the text and produce an object structure. The text must be wrapped in parens to avoid tripping on an ambiguity in JavaScript's syntax.

var myObject = eval('(' + myJSONtext + ')');

Update: Ah, I see, that's what the parentheses are for. Rats. Deleted the first part.

But this remains valid:

Don't use eval!

eval() is a dangerous function, which executes the code it's passed with the privileges of the caller. If you run eval() with a string that could be affected by a malicious party, you may end up running malicious code on the user's machine with the permissions of your webpage / extension. More importantly, third party code can see the scope in which eval() was invoked, which can lead to possible attacks in ways of which the similar Function is not susceptible.

Source: Mozilla JavaScript Reference: eval()

http://www.jsonlint.com/ this site has good JSON string validation which you should have at your disposal all the times. It's good to validate the JSON string when its really big.

Also do not user the eval() to get the JSON object. Visit http://www.json.org/ it has really nice guide lines check it.

There are many JavaScript libraries today which offers JSON API. I will suggest you to user one of it for safety.

http://api.jquery.com/jQuery.getJSON/

http://developer.yahoo.com/yui/json/

http://dojotoolkit.org/reference-guide/dojo/_base/json.html