javascript属性non enumerable仍然可以找到... in

Question

I'm writing a little javascript library: I've defined an Item object, then added a function with Item.prototype.addNumber and finally I set it as not enumerable, but if I try to log Item's method using for...in loop the function still appears. This is my code, Am I doing something wrong? (tested on Chrome 18 and Firefox 11)

function Item() {
    ...
}

Item.prototype.addString= function() {
    ...
}

Object.defineProperty(Item, "addString", { enumerable: false });

Answer 1

You're defining the property on Item instead of on Item.prototype .

Object.defineProperty(Item.prototype, "addString", { enumerable: false });

---

If you used Object.defineProperty to initially add addString to Item.prototype , then you could explicitly (or implicitly) set the property descriptors at the same time...

This will implicitly set enumerable:false , as well as false for configurable and writable .

Object.defineProperty(Item.prototype, "addString", { 
    value: function() {
        ...
    }
});

Or if you wanted only enumerable to be false , you could do this...

Object.defineProperty(Item.prototype, "addString", { 
    value: function() {
        ...
    },
    configurable: true,
    writable: true
//  ,enumerable: false  // uncomment to be explicit, though not necessary
});

Answer 2

You are defining a property ( addString ) directly on Object (the non enumerable one) and another addString (enumerable by default) on the Item 's prototype.

A for ( in ) iterates over properties up the prototype chain, that's why it appears there.