用Javascript嵌套对象-匿名不是函数错误

Question

Ok, so I'm a complete newbie to OOP in Javascript, apparently. I thought I understood it, but it appears I only know a small portion. Anyway, what I'm trying to do is setup an object to store and return data from an XML input by using a fairly simple string to retrieve data. I'd like to retrieve the data with a string similar to reader.getItem().getSubItem() or something like that.

Below is an example of what I attempted, but I get the error anonymous is not a function each time I try to do a call to fr.getType().isTexture() so obviously, I need to change something.

//Create the object by passing an XML element containing sub-elements
var fr = new FeatureReader(test.child(i));

alert(fr.getName()); //returns the object's name
alert(fr.getType().isTexture()); //"anonymous is not a function" error

function FeatureReader(feature) {
    var feat = feature;
    this.getName = function() {
        return feat.name;
    };
    this.getType = new function() {
        this.isTexture = new function() {
            if (feat.type.texture == "yes") {
                return true;
            }
            return false;
        };
        this.isModel = new function() {
            if (feat.type.model == "yes") {
                return true;
            }
            return false;
        };
    };
}

Now, obviously I could just remove the surrounding this.getType = function() {} around the this.isTexture and this.isModel to get my data, but for the sake of learning something, I'd like to see how it is recommended that I set this object up to get the returned values using a string similar to what I mentioned in the first and second paragraphs.

Answer 1

When you do this:

    this.isTexture = new function() {
        if (feat.type.texture == "yes") {
            return true;
        }
        return false;
    };

you're setting the "isTexture" property to the object constructed, not to that function. If you drop the new keyword from the statement, you'll be setting "isTexture" to be a function.

An expression of the form new <some-function> evaluates to an object, in other words.

edit — your "getType" property will also be an object, for the same reason. However, I think this would work:

alert( fr.getType.isTexture() );

Also note that your if statement can be simplified:

  return feat.type.texture == "yes";

Answer 2

What you can do is simply assign an object instead of using new :

function FeatureReader(feature) {
    var feat = feature;
    this.getName = function() {
        return feat.name;
    };
    this.getType = {
        isTexture: function() {
            return feat.type.texture == "yes";
        },
        isModel: function() {
            return feat.type.model == "yes";
        }
    };
}

Then use the method like:

instance.getType.isTexture()

Note that you don't need to return true or false , as returning an expression that evaluates to boolean like a == b returns a boolean value.