javascript: how to access static properties

问题

I want to access a static property using an instance. Something like this

function User(){
    console.log('Constructor: property1=' + this.constructor.property1) ;
}
User.prototype = {
    test: function() {
        console.log('test: property1=' + this.constructor.property1) ;
    }
}    
User.property1 = 10 ;   // STATIC PROPERTY

var inst = new User() ;
inst.test() ;

Here is the same code in a jsfiddle

In my situation I don't know which class the instance belongs to, so I tried to access the static property using the instance 'constructor' property, without success :( Is this possible ?

回答1:

so I tried to access the static property using the instance 'constructor' property

That's the problem, your instances don't have a constructor property - you've overwritten the whole .prototype object and its default properties. Instead, use

User.prototype.test = function() {
    console.log('test: property1=' + this.constructor.property1) ;
};

And you also might just use User.property1 instead of the detour via this.constructor. Also you can't ensure that all instances on which you might want to call this method will have their constructor property pointing to User - so better access it directly and explicitly.

回答2:

function getObjectClass(obj) {
    if (obj && obj.constructor && obj.constructor.toString) {
        var arr = obj.constructor.toString().match(
            /function\s*(\w+)/);

        if (arr && arr.length == 2) {
            return arr[1];
        }
    }

    return undefined;
}

function User(){
     console.log('Constructor: property1=' + this.constructor.property1) ;
 }

User.property1 = 10 ;

var inst = new User() ;

alert(getObjectClass(inst));

http://jsfiddle.net/FK9VJ/2/

回答3:

Perhaps you may have a look at: http://jsfiddle.net/etm2d/

User.prototype = {
test: function() {
    console.log('test: property1=' + this.constructor.property1) ;
    }
}

seems to be problematic, although i haven't yet figured out why.

来源：https://stackoverflow.com/questions/16345006/javascript-how-to-access-static-properties

标签

javascript

properties

static