Why this JavaScript property returns empty string, while JavaScript function works fine?

问题

Consider this simple JavaScript module pattern:

var human = (function () {
    var _name = '';
    return {
        name: _name,
        setName: function (name) {
            _name = name;
        }
    }
})();
human.setName('somebody');
alert(human.name); // shows an empty string
human = (function () {
    var _name = '';
    return {
        name: function() {
            return _name;
        },
        setName: function (name) {
            _name = name;
        }
    }
})();
human.setName('somebody');
alert(human.name()); // shows 'somebody'

Why the second closure works fine, while the first closure is not working? See example here.

Please also see this fiddle, which proves that simple properties can be used instead of getter functions.

回答1:

In Javascript

Strings and primitive types (boolean and numeric) are passed by value
Objects, arrays, and functions are passed by reference

As name is a string name: _name will store the current value of _name and not the reference to _name.

setName in your example will modify only _name.

getName will access _name which holds the current value.

.name will access the copied value which was set during the initialisation (name: _name).

See also SO: Javascript by reference vs. by value

回答2:

Try with this:

var human = (function () {
    var _name = '';
    var returnObj = {};
    returnObj.name = _name;
    returnObj.setName = function (name) {
        _name = name;
        returnObj.name = name;
    };

    return returnObj;
})();
human.setName('somebody');
alert(human.name);

The problem with your code was that setName was assigning a value to the _name variable and you ware accessing the name property of the returned object.

来源：https://stackoverflow.com/questions/14707532/why-this-javascript-property-returns-empty-string-while-javascript-function-wor

标签

javascript

properties

closures

getter-setter