What is the correct way to write HTML using Javascript?

Question

I see in some posts that people frown upon using document.write() in javascript when writing dynamic HTML.

Why is this? and what is the correct way?

Answer 1

document.write() doesn't work with XHTML. It's executed after the page has finished loading and does nothing more than write out a string of HTML.

Since the actual in-memory representation of HTML is the DOM, the best way to update a given page is to manipulate the DOM directly.

The way you'd go about doing this would be to programmatically create your nodes and then attach them to an existing place in the DOM. For [purposes of a contrived] example, assuming that I've got a div element maintaining an ID attribute of "header," then I could introduce some dynamic text by doing this:

// create my text
var sHeader = document.createTextNode('Hello world!');

// create an element for the text and append it
var spanHeader = document.createElement('span');
spanHeader.appendChild(sHeader);

// grab a reference to the div header
var divHeader = document.getElementById('header');

// append the new element to the header
divHeader.appendChild(spanHeader);

Answer 2

You can change the innerHTML or outerHTML of an element on the page instead.

Answer 3

The document.write method is very limited. You can only use it before the page has finished loading. You can't use it to update the contents of a loaded page.

What you probably want is innerHTML.

Answer 4

I'm not particularly great at JavaScript or its best practices, but document.write() along with innerHtml() basically allows you to write out strings that may or may not be valid HTML; it's just characters. By using the DOM, you ensure proper, standards-compliant HTML that will keep your page from breaking via plainly bad HTML.

And, as Tom mentioned, JavaScript is done after the page is loaded; it'd probably be a better practice to have the initial setup for your page to be done via standard HTML (via .html files or whatever your server does [i.e. php]).

Answer 5

document.write() will only work while the page is being originally parsed and the DOM is being created. Once the browser gets to the closing tag and the DOM is ready, you can't use document.write() anymore.

I wouldn't say using document.write() is correct or incorrect, it just depends on your situation. In some cases you just need to have document.write() to accomplish the task. Look at how google analytics gets injected into most websites.

After DOM ready, you have two ways to insert dynamic HTML (assuming we are going to insert new html into <div id="node-id"></div>):

1- using innerHTML on a node-

var node = document.getElementById('node-id');
node.innerHTML('<p>some dynamic html</p>');

2- using DOM methods-

var node = document.getElementById('node-id');
var newNode = document.createElement('p');
newNode.appendChild(document.createTextNode('some dynamic html'));
node.appendChild(newNode);

Using the DOM API methods might be the purist way to do stuff, but innerHTML has been proven to be much faster and is used under the hood in js libraries such as jQuery.

Answer 6

There are many ways to write html with JavaScript.

document.write is only useful when you want to write to page before it has actually loaded. If you use document.write() after the page has loaded (at onload event) it will create new page and overwrite the old content. Also it doesn't work with XML, that includes XHTML.

From other hand other methods can't be used before DOM has been created (page loaded), because they work directly with DOM.

These methods are:

• node.innerHTML = "Whatever";
• document.createElement('div'); and node.appendChild(), etc..

In most cases node.innerHTML is better since it's faster then DOM functions. Most of the time it also make code more readable and smaller.

Answer 7

I think you should use, instead of document.write, DOM javascript api like document.createElement, .createTextNode, .appendChild and similar. Safe and almost cross browser.

ihunger's outerHTML is not cross browser, IE only

Answer 8

1. DOM methods, as outlined by Tom.

2. innerHTML, as mentioned by iHunger.

DOM methods are highly preferable to strings for setting attributes and content. If you ever find yourself writing innerHTML= '<a href="'+path+'">'+text+'</a>' you're actually creating new cross-site-scripting security holes on the client side, which is a bit sad if you've spent any time securing your server-side.

DOM methods are traditionally described as ‘slow’ compared to innerHTML. But this isn't really the whole story. What is slow is inserting a lot of child nodes:

 for (var i= 0; i<1000; i++)
     div.parentNode.insertBefore(document.createElement('div'), div);

This translates to a load of work for the DOM finding the right place in its nodelist to insert the element, moving the other child nodes up, inserting the new node, updating the pointers, and so on.

Setting an existing attribute's value, or a text node's data, on the other hand, is very fast; you just change a string pointer and that's it. This is going to be much faster than serialising the parent with innerHTML, changing it, and parsing it back in (and won't lose your unserialisable data like event handlers, JS references and form values).

There are techniques to do DOM manipulations without so much slow childNodes walking. In particular, be aware of the possibilities of cloneNode, and using DocumentFragment. But sometimes innerHTML really is quicker. You can still get the best of both worlds by using innerHTML to write your basic structure with placeholders for attribute values and text content, which you then fill in afterwards using DOM. This saves you having to write your own escapehtml() function to get around the escaping/security problems mentioned above.

Answer 9

Perhaps a good idea is to use jQuery in this case. It provides handy functionality and you can do things like this:

$('div').html('<b>Test</b>');

Take a look at http://docs.jquery.com/Attributes/html#val for more information.

Answer 10

Surely the best way is to avoid doing any heavy HTML creation in your JavaScript at all? The markup sent down from the server ought to contain the bulk of it, which you can then manipulate, using CSS rather than brute force removing/replacing elements, if at all possible.

This doesn't apply if you're doing something "clever" like emulating a widget system.

Answer 11

How to set properties of the newly added child node. For eg. in the mentioned illustration

var sHeader = document.createTextNode('Hello world!');

var spanHeader = document.createElement('span');

spanHeader.appendChild(sHeader);

document.body.appendChild(spanHeader);

How can we change the "style.display" of the newly added 'span' element? The approach :

spanHeader.style.display = 'none'

does not work. Neither the following code works :

var newEle = document.getElementById('spanHeader');