Question

I have figure out this code

function getAllProperties(obj){
    var result={
        properties:[],
        methods:[]
    };
    var proto = obj;
    while(proto !== null){
        var props = Object.getOwnPropertyNames(proto);
        props.forEach(function(v){
            typeof proto[v] === "function" ? result.methods.push(v) : result.properties.push(v);
        });
        proto = Object.getPrototypeOf(proto);
    }
    return result;
}

And the parameter I passed in is canvas context object(obtain by canvas.getContext(‘2d’)).The code words fine with Chrome . But it comes out that firefox get the ‘Illegal operation on WrappedNative prototype object’ Error . Can anyone tell me what’s wrong with it?

Answer 1

When you write proto[v] you might actually invoke property accessor functions (for example if the property has been defined with a get/set as per HTML5) without an actual instance context. This causes the error.

Try getting Object.getOwnPropertyDescriptor to access the property without actually invoking it. The result might have a value property or a get/set property that are actually invoked when you access the field.