Differencebetween Document and Document in JavaScript

What is the difference between Document and document?

document is the actual object for your html page loaded in browser. This is a DOM object.

Document is the function(a DOM interface precisely), which will be used to create the document object. This "Document" is implemented by the browser program. This takes our HTML file as input and creates the "document" object.

Document.getElementById(..) -> wrong. This wont work.
Document.prototype.getElementById(..) This is the right way

Refer this link - Reference link
Document Implementation is specific to each browser. But it can be extended. Check this article too.
http://perfectionkills.com/whats-wrong-with-extending-the-dom/

The document object could be from separate implementations by browsers based on the file type. For HTML the prototype would be "HTMLDocumentPrototype" (uses Document interface), and for XML it would be just a "Object" and no prototype attached. This might differ from browser to browser, since implementation is specific.

What is the difference between Document and document in JavaScript?

What is the difference between Document and document?

document (or window.document) is a reference to the document contained in the window. (spec)

Document is the DOM interface for documents, which is exposed on the global object. (spec, spec)

How does one use Document (as it is not a function, therefore, not constructable)?

It's a host object and does not need to follow the EcmaScript spec - yet that does not mean it's not a function. It may differ from browser to browser as well. Yet it is not intended to be called (if you try it you'll get a NOT_SUPPORTED_ERR), there are other methods to instantiate/obtain new documents. What you can still use it for is

> document instanceof Document
true
> Document.prototype
DocumentPrototype {
    adoptNode: Function
    constructor: Document
    createAttribute: Function
    …
    querySelector: Function
    querySelectorAll: Function
}
|- NodePrototype
|- Object

so you could extend its prototype and use those methods on all XMLDocuments/HTMLDocuments in your app (but only if you know what’s wrong with extending the DOM).

Most importantly, what is the harm in "monkey-patching" Document to make it constructable?

I'm not sure how you would do that. Overwriting it could harm every script that expects it to work as above (unless you fix the prototype property of your new function). And maybe the Document property of window is non-writable in some environments, so you could harm yourself.

What is the difference between window, screen, and document in JavaScript?

window is the main JavaScript object root, aka the global object in a browser, and it can also be treated as the root of the document object model. You can access it as window.

window.screen or just screen is a small information object about physical screen dimensions.

window.document or just document is the main object of the potentially visible (or better yet: rendered) document object model/DOM.

Since window is the global object, you can reference any properties of it with just the property name - so you do not have to write down window. - it will be figured out by the runtime.

Difference between document and window in the DOM?

The window command are the Web APIs that the browser has. It is always executed last because it is not Javascript and therefore the event loop will prioritize your JavaScript commands first. The document, on the other hand, is used for DOM manipulation to modify the HTML.

JavaScript: Whats the difference between 'Document' and 'HTML'

I'll answer the question in several parts.

In JavaScript (not just jQuery, but all JavaScript) the document keyword is a handle on the object that contains the HTMLDocument. You might use this handle in the following scenarios...

// Get the current web address
alert(document.location.href);

When you pass the document to jQuery, it parses the document into a jQuery object.

When you pass the "html" selector to jQuery, it uses this string to find any elements in the document object model that match the selector (in all cases, there will be one html element).

In reality, you won't notice a difference in behaviour between these:

$(document).click(function() { alert('blah'); });   
$('html').click(function() { alert('blah'); });
$('body').click(function() { alert('blah'); });

But the technical difference is that document is an object and 'html' is a string that is used to search for an element. Both the object and any matching elements are converted into jQuery objects.

As they all add a click event handler to the "visible" part of the page, which is the only part of the page a user can realistically click on.

What is difference between $(document) and $('*') and how to make sure $ reference is assigned to which library?

$ in jQuery is basically Syntatic Sugar which means developers love to assign $ as shorthand for different library. In this case $ is shorthand of jQuery or window.jQuery.

jQuery can be run in compatibility mode if another library is already using $. Just use jQuery.noConflict(); to know if there is. $ is pretty commonly used as a selector function in various JavaScript libraries.

Run jQuery.noConflict() method to give control of the $ variable back to whichever library first implemented it. This helps to make sure that jQuery doesn't conflict with the $ object of other libraries.

Here is simple way of avoiding any conflict:

// Import other Library
// Import jQuery Library
$.noConflict();
// Code that uses other library's $ can follow here.

This technique is especially effective in conjunction with the .ready() method's ability to alias the jQuery object, as within the .ready() we can use $ if we wish without fear of conflicts later:

// Import other library
// Import jQuery
$.noConflict();
jQuery(document).ready(function($) {
   // Code that uses jQuery's $ can follow here.
});
// Code that uses other library's $ can follow here.

As per jQuery documentation:

By default, jQuery uses "$" as shortcut for "jQuery"

having said that.

$(".class_name") or jQuery(".class_name") is the same.

Coming to next part of your question:

What is document ?

document is a Javascript internal DOM Object of the current webpage. In browser console you can go and invoke following:

document
It will return you whole DOM of page in Tree format.

> typeof(document)

<. object

So, typeof(document) returned object. Hence, document is a DOM object containing whole webpage sourcecode + many additional information in tree format.

What is $(document) ?

Similarly, $(document) is also an Object, in Array format having document and context of webpage.

What is $('*')?

It is also an object returned after jQuery process full DOM. It contains array of all the elements in the DOM so that jQuery can process it faster and return result
You can try in browser console.

> $('*')

> typeof($('*'))

What's the differences between document and window

A quick search on Google, or here on StackOverflow, would have found a stack of answers. These will help you understand the difference.

1. What is the difference between window, screen, and document in Javascript?

2. trying to understand the difference between window and document objects in js

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