JavaScript getter support in IE8

问题:

Check out this code. This is a very simple JavaScript object which is implemented using Module Pattern (and you can see the live example at this fiddle address)

var human = function() {
    var _firstName = '';
    var _lastName = ''
    return {
        get firstName() {
            return _firstName;
        }, get lastName() {
            return _lastName;
        }, set firstName(name) {
            _firstName = name;
        }, set lastName(name) {
            _lastName = name;
        }, get fullName() {
            return _firstName + ' ' + _lastName;
        }
    }
}();
human.firstName = 'Saeed';
human.lastName = 'Neamati';
alert(human.fullName);

However, IE8 doesn't support JavaScript get and set keywords. You can both test it and see MDN.

What should I do to make this script compatible with IE8 too?

回答1:

What should I do to make this script compatible with IE8 too?

Change it completely. For example, instead of using accessor properties, use a combination of normal properties and functions:

human.firstName = 'Saeed';
human.lastName  = 'Neamati';
alert(human.getFullName());

Somebody else suggested using a DOM object in IE and adding the properties using Object.defineProperty(). While it may work, I'd highly recommend against this approach for several reasons, an example being that the code you write may not be compatible in all browsers:

var human = document.createElement('div');
Object.defineProperty(human, 'firstName', { ... });
Object.defineProperty(human, 'lastName',  { ... });
Object.defineProperty(human, 'children',  { value: 2 });

alert(human.children);
//-> "[object HTMLCollection]", not 2

This is true of at least Chrome. Either way it's safer and easier to write code that works across all the browsers you want to support. Any convenience you gain from being able to write code to take advantage of getters and setters has been lost on the extra code you wrote specifically targeting Internet Explorer 8.

This is, of course, in addition to the reduction in performance, the fact that you will not be able to use a for...in loop on the object and the potential confusion ensuing when you use a property you thought you defined but was pre-existing on the DOM object.

回答2:

You cannot (as Andy answered)

The closest alternative would be

var human = function() {
    var _firstName = '';
    var _lastName = '';

    return {
        firstName: function() {
            if (arguments.length === 1) {
                _firstName = arguments[0];
            }
            else {
                return _firstName;
            }
        },
        lastName: function() {
            if (arguments.length === 1) {
                _lastName = arguments[0];
            }
            else {
                return _lastName;
            }
        },
        fullName: function() {
            return _firstName + ' ' + _lastName;
        }
    };
}();

human.firstName('Saeed');
human.lastName('Neamati');

alert(human.fullName());

Demo at http://jsfiddle.net/gaby/WYjqB/2/

回答3:

IE8 supports getters and setters on DOM nodes, so if you really want to have getters and setters, you can do this:

var objectForIe8 = $("<div></div>")[0];    
Object.defineProperty(objectForIe8, "querySelector", {
    get: function() {
        return this.name;
    },
    set: function(val) {
        this.name = val+", buddy";  
    }
});
// notice you can overwrite dom properties when you want to use that property name
objectForIe8.querySelector = "I'm not your guy"; 

alert(objectForIe8.querySelector);

Note this gives you a somewhat significant performance hit, so I wouldn't use this technique if you need to create thousands of objects like this. But if you're not worried about performance of this particular object, it'll tide you over. And if you couldn't care less about ie8 performance, and just want it to work, use this technique for ie8 only and you're golden : )

回答4:

Check it on http://robertnyman.com/2009/05/28/getters-and-setters-with-javascript-code-samples-and-demos/

The future, and ECMAScript standardized way, of extending objects in all sorts of ways is through Object.defineProperty. This is how Internet Explorer chose to implement getters and setters, but it is unfortunately so far only available in Internet Explorer 8, and not in any other web browser. Also, IE 8 only supports it on DOM nodes, but future versions are planned to support it on JavaScript objects as well.

You can find the test cases on the same site at http://robertnyman.com/javascript/javascript-getters-setters.html#object-defineproperty

Object.defineProperty(document.body, "description", {
    get : function () {
        return this.desc;
    },
    set : function (val) {
        this.desc = val;
    }
});
document.body.description = "Content container";

Result:

document.body.description = "Content container"