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How can i start a new line in javascript

document.getElementById("print").innerHTML = good;
I want to start writing on new line when using this function for the second time

Here is what I would recommend:
Define the element once at the beginning to save getting it every time.
Create a custom function called print() which you can call more easily.
Use += to add and not overwrite content.
Use br elements to add line breaks after each printed message.
printDiv = document.getElementById("print");
function print(text) {
printDiv.innerHTML += text + '<br>';
}
print('This text');
print('is just here');
print('to test the function');
<div id="print"></div>

You are generating HTML.
A new line in HTML is usually created with a <br> element.
That might not be the right option for the data you are generating though. HTML is a semantic markup language so you should generate the markup that describes the semantics of the data you are working with.
That might involve creating a list with list items in it, multiple paragraphs, or something else.

Adding Javascript variables to HTML elements

So, I have some code that should do four things:
remove the ".mp4" extension from every title
change my video category
put the same description in all of the videos
put the same keywords in all of the videos
Note: All of this would be done on the YouTube upload page. I'm using Greasemonkey in Mozilla Firefox.
I wrote this, but my question is: how do I change the HTML title in the actual HTML page to the new title (which is a Javascript variable)?
This is my code:
function remove_mp4()
{
var title = document.getElementsByName("title").value;
var new_title = title.replace(title.match(".mp4"), "");
}
function add_description()
{
var description = document.getElementsByName("description").value;
var new_description = "Subscribe."
}
function add_keywords()
{
var keywords = document.getElementsByName("keywords").value;
var new_keywords = prompt("Enter keywords.", "");
}
function change_category()
{
var category = document.getElementsByName("category").value;
var new_category = "<option value="27">Education</option>"
}
remove_mp4();
add_description();
add_keywords();
change_category();
Note: If you see any mistakes in the JavaScript code, please let me know.
Note 2: If you wonder why I stored the current HTML values in variables, that's because I think I will have to use them in order to replace HTML values (I may be wrong).

A lot of things have been covered already, but still i would like to remind you that if you are looking for cross browser compatibility innerHTML won't be enough, as you may need innerText too or textContent to tackle some old versions of IE or even using some other way to modify the content of an element.
As a side note innerHTML is considered from a great majority of people as deprecated though some others still use it. (i'm not here to debate about is it good or not to use it but this is just a little remark for you to checkabout)
Regarding remarks, i would suggest minimizing the number of functions you create by creating some more generic versions for editing or adding purposes, eg you could do the following :
/*
* #param $affectedElements the collection of elements to be changed
* #param $attribute here means the attribute to be added to each of those elements
* #param $attributeValue the value of that attribute
*/
function add($affectedElements, $attribute, $attributeValue){
for(int i=0; i<$affectedElements.length; i++){
($affectedElements[i]).setAttribute($attribute, $attributeValue);
}
}
If you use a global function to do the work for you, not only your coce is gonna be easier to maintain but also you'll avoid fetching for elements in the DOM many many times, which will considerably make your script run faster. For example, in your previous code you fetch the DOM for a set of specific elements before you can add a value to them, in other words everytime your function is executed you'll have to go through the whole DOM to retrieve your elements, while if you just fetch your elements once then store in a var and just pass them to a function that's focusing on adding or changing only, you're clearly avoiding some repetitive tasks to be done.
Concerning the last function i think code is still incomplete, but i would suggest you use the built in methods for manipulating HTMLOption stuff, if i remember well, using plain JavaScript you'll find yourself typing this :
var category = document.getElem.... . options[put-index-here];
//JavaScript also lets you create <option> elements with the Option() constructor
Anyway, my point is that you would better use JavaScript's available methods to do the work instead of relying on innerHTML fpr anything you may need, i know innerHTML is the simplest and fastest way to get your work done, but if i can say it's like if you built a whole HTML page using and tags only instead of using various semantic tags that would help make everything clearer.
As a last point for future use, if you're interested by jQuery, this will give you a different way to manipulate your DOM through CSS selectors in a much more advanced way than plain JavaScript can do.
you can check out this link too :
replacement for innerHTML

I assume that your question is only about the title changing, and not about the rest; also, I assume you mean changing all elements in the document that have "title" as name attribute, and not the document title.
In that case, you could indeed use document.getElementsByName("title").
To handle the name="title" elements, you could do:
titleElems=document.getElementsByName("title");
for(i=0;i<titleElems.length;i++){
titleInner=titleElems[i].innerHTML;
titleElems[i].innerHTML=titleInner.replace(titleInner.match(".mp4"), "");
}
For the name="description" element, use this: (assuming there's only one name="description" element on the page, or you want the first one)
document.getElementsByName("description")[0].value="Subscribe.";
I wasn't really sure about the keywords (I haven't got a YouTube page in front of me right now), so this assumes it's a text field/area just like the description:
document.getElementsByName("keywords")[0].value=prompt("Please enter keywords:","");
Again, based on your question which just sets the .value of the category thingy:
document.getElementsByName("description")[0].value="<option value='27'>Education</option>";
At the last one, though, note that I changed the "27" into '27': you can't put double quotes inside a double-quoted string assuming they're handled just like any other character :)
Did this help a little more? :)

Sry, but your question is not quite clear. What exactly is your HTML title that you are referring to?
If it's an element that you wish to modify, use this :
element.setAttribute('title', 'new-title-here');
If you want to modify the window title (shown in the browser tab), you can do the following :
document.title = "the new title";

You've reading elements from .value property, so you should write back it too:
document.getElementsByName("title").value = new_title

If you are refering to changing text content in an element called title try using innerHTML
var title = document.getElementsByName("title").value;
document.getElementsByName("title").innerHTML = title.replace(title.match(".mp4"), "");
source: https://developer.mozilla.org/en-US/docs/DOM/element.innerHTML

The <title> element is an invisible one, it is only displayed indirectly - in the window or tab title. This means that you want to change whatever is displayed in the window/tab title and not the HTML code itself. You can do this by changing the document.title property:
function remove_mp4()
{
document.title = document.title.replace(title.match(".mp4"), "");
}

How can I separately retrieve the HTML that's before and after a child element inside a parent element?

We're writing a web app that relies on Javascript/jQuery. It involves users filling out individual words in a large block of text, kind of like Mad Libs. We've created a sort of HTML format that we use to write the large block of text, which we then manipulate with jQuery as the user fills it out.
Part of a block of text might look like this:
<span class="fillmeout">This is a test of the <span>NOUN</span> Broadcast System.</span>
Given that markup, I need to separately retrieve and manipulate the text before and after the inner <span>; we're calling those the "prefix" and "suffix".
I know that you can't parse HTML with simple string manipulation, but I tried anyway; I tried using split() on the <span> and </span> tags. It seemed simple enough. Unfortunately, Internet Explorer casts all HTML tags to uppercase, so that technique fails. I could write a special case, but the error has taught me to do this the right way.
I know I could simply use extra HTML tags to manually denote the prefix and suffix, but that seems ugly and redundant; I'd like to keep our markup format as lean and readable and writable as possible.
I've looked through the jQuery docs, and can't find a function that does exactly what I need. There are all sorts of functions to add stuff before and after and around and inside elements, but none that I can find to retrieve what's already there. I could remove the inner <span>, but then I don't know how I can tell what came before the deleted element apart from what came after it.
Is there a "right" way to do what I'm trying to do?

With simple string manipulations you can also use Regex.
That should solve your problem.
var array = $('.fillmeout').html().split(/<\/?span>/i);

Use your jQuery API! $('.fillmeout').children() and then you can manipulate that element as required.
http://api.jquery.com/children/

For completeness, I thought I should point out that the cleanest answer is to put the prefix and suffix text in it's own <span> like this and then you can use jQuery selectors and methods to directly access the desired text:
<span class="fillmeout">
<span class="prefix">This is a test of the </span>
<span>NOUN</span>
<span class="suffix"> Broadcast System.</span>
</span>
Then, the code would be as simple as:
var fillme = $(".fillmeout").eq(0);
var prefix = fillme.find(".prefix").text();
var suffix = fillme.find(".suffix").text();
FYI, I would not call this level of simplicity "ugly and redundant" as you theorized. You're using HTML markup to delineate the text into separate elements that you want to separately access. That's just smart, not redundant.
By way of analogy, imagine you have toys of three separate colors (red, white and blue) and they are initially organized by color and you know that sometime in the future you are going to need to have them separated by color again. You also have three boxes to store them in. You can either put them all in one box now and manually sort them out by color again later or you can just take the already separated colors and put them each into their own box so there's no separation work to do later. Which is easier? Which is smarter?
HTML elements are like the boxes. They are containers for your text. If you want the text separated out in the future, you might as well put each piece of text into it's own named container so it's easy to access just that piece of text in the future.

Several of these answers almost got me what I needed, but in the end I found a function not mentioned here: .contents(). It returns an array of all child nodes, including text nodes, that I can then iterate over (recursively if needed) to find what I need.

I'm not sure if this is the 'right' way either, but you could replace the SPANs with an element you could consistently split the string on:
jQuery('.fillmeout span').replaceWith('|');
http://api.jquery.com/replaceWith/
http://jsfiddle.net/mdarnell/P24se/

You could use
$('.fillmeout span').get(0).previousSibling.textContent
$('.fillmeout span').get(0).nextSibling.textContent
This works in IE9, but sadly not in IE versions smaller than 9.

Based on your example, you could use your target as a delimiter to split the sentence.
var str = $('.fillmeout').html();
str = str.split('<span>NOUN</span>');
This would return an array of ["This is a test of the ", " Broadcast System."]. Here's a jsFiddle example.

You could just use the nextSibling and previousSibling native JavaScript (coupled with jQuery selectors):
$('.fillmeout span').each(
function(){
var prefix = this.previousSibling.nodeValue,
suffix = this.nextSibling.nodeValue;
});
JS Fiddle proof of concept.
References:
each().
node.nextSibling.
node.previousSibling.

If you want to use the DOM instead of parsing the HTML yourself and you can't put the desired text in it's own elements, then you will need to look through the DOM for text nodes and find the text nodes before and after the span tag.
jQuery isn't a whole lot of help when dealing with text nodes instead of element nodes so the work is mostly done in plain javascript like this:
$(".fillmeout").each(function() {
var node = this.firstChild, prefix = "", suffix = "", foundSpan = false;
while (node) {
if (node.nodeType == 3) {
// if text node
if (!foundSpan) {
prefix += node.nodeValue;
} else {
suffix += node.nodeValue;
}
} else if (node.nodeType == 1 && node.tagName == "SPAN") {
// if element and span tag
foundSpan = true;
}
node = node.nextSibling;
}
// here prefix and suffix are the text before and after the first
// <span> tag in the HTML
// You can do with them what you want here
});
Note: This code does not assume that all text before the span is located in one text node and one text node only. It might be, but it also might not be so it collates all the text nodes together that are before and after the span tag. The code would be simpler if you could just reference one text node on each side, but it isn't 100% certain that that is a safe assumption.
This code also handles the case where there is no text before or after the span.
You can see it work here: http://jsfiddle.net/jfriend00/P9YQ6/

Remove formatting tags from string body of email

How do you remove all formatting tags when calling:
GmailApp.getInboxThreads()[0].getMessages()[0].getBody()
such that the only remainder of text is that which can be read.
Formatting can be destroyed; the text in the body is only needed to be parsed, but tags such as:
"&"
<br>
and possibly others, need to be removed.

Even though there's no DOM in Apps Script, you can parse out HTML and get the plain text this way:
function getTextFromHtml(html) {
return getTextFromNode(Xml.parse(html, true).getElement());
}
function getTextFromNode(x) {
switch(x.toString()) {
case 'XmlText': return x.toXmlString();
case 'XmlElement': return x.getNodes().map(getTextFromNode).join('');
default: return '';
}
}
calling
getTextFromHtml("hello <div>foo</div>& world <br /><div>bar</div>!");
will return
"hello foo& world bar!".
To explain, Xml.parse with the second param as "true" parses the document as an HTML page. We then walk the document (which will be patched up with missing HTML and BODY elements, etc. and turned into a valid XHTML page), turning text nodes into text and expanding all other nodes.
This is admittedly poorly documented; I wrote this by playing around with the Xml object and logging intermediate results until I got it to work. We need to document the Xml stuff better.

I noticed you are writing a Google Apps Script. There's no DOM in Google Apps Script, nor you can create elements and get the innerText property.
getBody() gives you the email's body in HTML. You can replace tags with this code:
var html = GmailApp.getInboxThreads()[0].getMessages()[0].getBody();
html=html.replace(/<\/div>/ig, '\n');
html=html.replace(/<\/li>/ig, '\n');
html=html.replace(/<li>/ig, ' *');
html=html.replace(/<\/ul>/ig, '\n');
html=html.replace(/<\/p>/ig, '\n');
html=html.replace(/<br\/?>/ig, '\n');
html=html.replace(/<[^>]+>/ig, '');
May be you can find more tags to replace. Remember this code isn't for any HTML, but for the getBody() HTML. GMail has its own way to format de body, and doesn't use every possible existing tag in HTML, only a subset of it; then our GMail specific code is shorter.

I found an easier way to accomplish this task.
Use the htmlBody advanced argument within the arguments of sendEmail(). Heres an example:
var threads = GmailApp.search ('is:unread'); //searches for unread messages
var messages = GmailApp.getMessagesForThreads(threads); //gets messages in 2D array
for (i = 0; i < messages.length; ++i)
{
j = messages[i].length; //to process most recent conversation in thread (contains messages from previous conversations as well, reduces redundancy
messageBody = messages[i][j-1].getBody(); //gets body of message in HTML
messageSubject = messages [i][j-1].getSubject();
GmailApp.sendEmail("dummyuser#dummysite.com", messageSubject, "", {htmlBody: messageBody});
}
First I find all the threads containing unread messages. Then I get the messages contained within the threads into a two dimensional array using the getMessagesForThreads() method within GmailApp. Then I created a for loop that runs for all of the threads I found. I set j equal to the threads message count so I can send only the most recent message on the thread (j-1). I get the HTML body of the message with getBody() and the subject through getSubject(). I use the sendEmail(recipients, subject, body, optAdvancedArgs) to send the email and process the HTML body. The result is an email sent properly formatted with all features of HTML included. The documentation for these methods can be found here: https://developers.google.com/apps-script/service_gmail
I hope this helps, again the manual parsing method does work, but I still found bits and pieces of HTML left hanging around so I thought I would give this a try, It worked for me, if I find any issues in the longrun I will update this post. So far so good!

Google now has the getPlainBody() function that will get the plain text from the body of an email. It is in the text class.
I had been using a script to send emails to convert them to tasks and google broke it with a change to the functionality of Corey's answer above. I've replaced it with the following.
var taskNote = ((thread.getMessages()[0]).getPlainBody()).substring(0,1000);

I am not sure what you mean by .getBody() - is this supposed to return a DOM body element?
However, the simplest solution for removing HTML tags is probably to let the browser render the HTML and ask him for the text content:
var myHTMLContent = "hello & world <br />!";
var tempDiv = document.createElement('div');
tempDiv.innerHTML = myHTMLContent;
// retrieve the cleaned content:
var textContent = tempDiv.innerText;
With the above example, the textContent variable will contain the text
"hello & world
!"
(Note the line break due to the <br /> tag.)

Best way to pick up text in a HTML element that is in the parent node only

I have, for example, markup like this
<div id="content">
<p>Here is some wonderful text, and here is a link. All links should have a `href` attribute.</p>
</div>
Now I want to be able to perform some regex replace on the text inside the p element, but not in any HTML, i.e. be able to match the href within backticks, but not inside the anchor element.
I thought about regex, but as the general consensus is, I shouldn't be using them to parse HTML.
My current method of doing this is like so: I've got a bunch of words in an array, and I am looping through them and making an object of data like so:
termsData[term] = {
regex: new RegExp('(\\b' + term + '\\b)', 'gmi'),
replaceWith: '<span>{TERM}</span>'
};
I then loop through it again, making the replacements like so:
var html = obj.html();
$.each(terms, function(i, term) {
// Replace each word in the HTML with the span
html = html.replace(termsData[term].regex, termsData[term].replaceWith.replace(/{TERM}/, '$1'));
});
obj.html(html);
Now I did a lot of this last night at an ungodly hour, and copying and pasting it into here seems to make think I should refactor some of this.
So from you should be able to tell, I want to be able to replace plain text, but not anything inside a HTML tag.
What would be the best way to do it?
Note: The source code is coming from here if you'd like a better look.

You're right to not want to be processing HTML with regex. It's also bad news to be assigning huge chunks of .html(); apart from the performance drawbacks of serialising and reparsing a large amount of HTML, you'll also lose unserialisable data like event listeners, form data and JS properties/references.
See the findText function in this answer and call something like (assuming obj is a jQuery wrapper over your topmost node to search in):
findText(obj[0], /\b(term1|term2|term3)\b/g, function(node, match) {
var span= document.createElement('span');
node.splitText(match.index+match[0].length);
span.appendChild(node.splitText(match.index));
node.parentNode.insertBefore(span, node.nextSibling);
});