How to inspect Javascript Objects

Question

How can I inspect an Object in an alert box? Normally alerting an Object just shows an opaque representation like [object Object]. For example:

alert(document); // displays "[object HTMLDocument]"

But I want to get the properties and methods of the object in the alert box. How can I achieve this functionality, if possible? Or are there any other suggestions?

Particularly, I am seeking a solution for a production environment where console.log and Firebug are not available.

Answer 1

The for-in loops for each property in an object or array. You can use this property to get to the value as well as change it.

Note: Private properties are not available for inspection, unless you use a "spy"; basically, you override the object and write some code which does a for-in loop inside the object's context.

For in looks like:

for (var property in object) loop();

Some sample code:

function xinspect(o,i){
    if(typeof i=='undefined')i='';
    if(i.length>50)return '[MAX ITERATIONS]';
    var r=[];
    for(var p in o){
        var t=typeof o[p];
        r.push(i+'"'+p+'" ('+t+') => '+(t=='object' ? 'object:'+xinspect(o[p],i+'  ') : o[p]+''));
    }
    return r.join(i+'\n');
}

// example of use:
alert(xinspect(document));

Edit: Some time ago, I wrote my own inspector, if you're interested, I'm happy to share.

Edit 2: Well, I wrote one up anyway.