Question

As I am jumping into Javascript a little deeper, I got this odd result when trying a test.

function CustomeObject() {
    this.type = "custom";
};
var node1 = document.createTextNode(Date.prototype);
var node2 = document.createTextNode(CustomeObject.prototype);

document.getElementsByTagName("body")[0].appendChild(node1);
document.getElementsByTagName("body")[0].appendChild(node2);

And the result is as follow:

Invalid Date [object Object]

As I read from one source on the internet and it says: the prototype is a buil-in property of any object, and it’s actually an object itself. But this test failed with the Date Object.
Could you tell me what wrong with my code to test Date prototype property?
Thank you!

Answer 1

When you pass Date.prototype to document.createTextNode() it will implicitly call toString() on the passed object.

The default output of toString() is [object Object], as seen in your second test.

However Date.prototype has its own toString() function whose purpose is to return the current Date object (i.e. this) as text.

var now = new Date();
console.log(now.toString()); // outputs current date
console.log(now);            // does the same due to implicit toString() call

When you call that function directly its this pointer incorrectly contains Data.prototype instead of a date object, hence the "Invalid Date" output.