javascript: get all object parameters

Question

I have a JS object with a variable number of parameters. Is there a way to see what parameters have been passed this particular time?

The example:

function getElement() {
    var scope = document;

    this.by = function(data){
        if (data.id)    scope = scope.getElementById(data.id);
        if (data.tag)   scope = scope.getElementsByTagName(data.tag);       
        return scope;
    }
}

And I run it like so

var x = new getElement(); 
vad div = x.by({id : "chosenID"});

gets the div with the id chosenID

or

var x = new getElement(); 
vad inputs = x.by({id : "chosenID", tag : "input"});

gets all the inputs in the div with the id chosenID;

I want to know if I passed one or two parameters, and which ones.

Thanks!

ps: I appreciate your time in helping me out, but please do not sugget jQuery or other JS framework as this is for learning purposes only. Much obliged, Sorin.

Answer 1

Use a for … in loop to iterate over the passed object's parameters, like:

var prop;

for (prop in data) {
    if (data.hasOwnProperty(prop)) {
        // do something with data[prop]
    }
}

Don't forget to check the property with hasOwnProperty.

Answer 2

Using object iteration (key in data) and array-combining... you can return a number of elements... although the object iteration is rendered pretty useless by by the switch statement.

function getElement() {
    var scope = document;
    this.by = function(data){
        var key;
        var ret=[];
        for (key in data) {
          if(data.hasOwnProperty(key)) {
            switch(key) {
              case "id":
                ret=ret.concat(scope.getElementById(data[key]));
                break;
              case "tag":
                ret=ret.concat(scope.getElementsByTagName(data[key]));
                break;
              default:
                throw new Error("Unknown property "+key);
            }
          }
        }
        return ret;
    };
}