If you write script that has a lot String content mixed with variables, I'm sure you're doing a lot of heavy concatenation.
Building string combos with quotes and apostrophes sprinkled all over a script gets confusing. The way I like to keep this confusion to a minimum is to write my static markup separately. This allows me to make sure it shows up as intended. Then I concatenate my variables in all the places that need to have dynamic content.

Taking static markup or script and wrapping quotes around every line is a chore so I made this Concatenation Tool to help with that.

Currently I've only made this support languages I'm using mostly. If I have to use a new language I'd just add it in.

Below are some basic use case examples of where a concatenation tool can be useful.

JavaScript
Concatenating a content to add to a Jquery UI Dialog.
In this example I purposely used he "text()" method to show the XML content instead of "html()".

    <script type="text/javascript">
                $(document).ready(function(){
                var ns = "";
                ns += "<LIBRARY>";
                ns += "    <BOOK>";
                ns += "        <TITLE id=\"2356\">Charlotte's Web</TITLE>";
                ns += "        <AUTHOR>E. B. White</AUTHOR>";
                ns += "        <FAMOUS_SAYING>\"Always be on the lookout for the presence of wonder.\"</FAMOUS_SAYING>";
                ns += "    </BOOK>";
                ns += "    <BOOK>";
                ns += "        <TITLE id=\"95\">Scuffy the Tugboat</TITLE>";
                ns += "        <AUTHOR>Gertrude Crampton</AUTHOR>";
                ns += "        <FAMOUS_SAYING>\"Toot, tooot!\" cried the frightened tugboat.</FAMOUS_SAYING>";
                ns += "    </BOOK>";
                ns += "</LIBRARY>";
                $("#myDialog").dialog({width:400, height:400});
                $("#myDialog p").text(ns);
                });
    </script>

Python
Concatenating with qoutes

ns = ""
ns += "<LIBRARY>"
ns += "    <BOOK>"
ns += "        <TITLE id=\"2356\">Charlotte's Web</TITLE>"
ns += "        <AUTHOR>E. B. White</AUTHOR>"
ns += "        <FAMOUS_SAYING>\"Always be on the lookout for the presence of wonder.\"</FAMOUS_SAYING>"
ns += "    </BOOK>"
ns += "    <BOOK>"
ns += "        <TITLE id=\"95\">Scuffy the Tugboat</TITLE>"
ns += "        <AUTHOR>Gertrude Crampton</AUTHOR>"
ns += "        <FAMOUS_SAYING>\"Toot, tooot!\" cried the frightened tugboat.</FAMOUS_SAYING>"
ns += "    </BOOK>"
ns += "</LIBRARY>"
print(ns)

Python concatenation with triple quotes to preserve the carriage returns

ns="""<LIBRARY>
    <BOOK>
        <TITLE id="2356">Charlotte's Web</TITLE>
        <AUTHOR>E. B. White</AUTHOR>
        <FAMOUS_SAYING>"Always be on the lookout for the presence of wonder."</FAMOUS_SAYING>
    </BOOK>
    <BOOK>
        <TITLE id="95">Scuffy the Tugboat</TITLE>
        <AUTHOR>Gertrude Crampton</AUTHOR>
        <FAMOUS_SAYING>"Toot, tooot!" cried the frightened tugboat.</FAMOUS_SAYING>
    </BOOK>
</LIBRARY>"""
print(ns)

Concatenation with regular quotes

Concatenation of blocks of text with triple quotes

JSFL
Concatenating a XUL markup string for building Flash IDE Panel with JSFL.

if(fl.documents.length == 0){
	fl.createDocument("timeline");
}
//------------------------------------------------------------
//An existing folder for the panel's source to be written to.
//------------------------------------------------------------
var appFolderName="jsflUI_sample";
var date=new Date();
function writePanelSource()
{
	var code = '';
	code += '<overlay>';
	code += '	<dialog id="app" title="Sample UI">';
	code += '		<hbox>';
	code += '			<spacer/>';
	code += '			<button id="b0" label="Button"/>';
	code += '		</hbox>';
	code += '		<separator/>';
	code += '		<vbox>';
	code += '			<label control="f0" value="Field 1" align="left"/>';
	code += '			<textbox id="f0" size="50" value="'+date.toString()+'"/>';
	code += '			<label control="f1" value="Field 2:" align="left"/>';
	code += '			<textbox id="f1" size="50" value=""/>';
	code += '		</vbox>';
	code += '		<checkbox id="cb0" label="Checkbox 1" checked="false" />';
	code += '		<checkbox id="cb1" label="Checkbox 2" checked="false" />';
	code += '	</dialog>';
	code += '</overlay>';
	FLfile.write(fl.configURI + "Commands/"+appFolderName+"/panelsource.xml", code);
	return code;
}

//----------------------------------------------------------------
//Writes the markup to "appFolderName" of Flash's "Commands folder
//----------------------------------------------------------------
writePanelSource();

//-------------------------------
//Open the Panel in Flash's IDE
//-------------------------------
fl.getDocumentDOM().xmlPanel(fl.configURI + "Commands/"+appFolderName+"/panelsource.xml");

Panel UI dialog from JSFL

SharePoint
Concatenating CAML querys.

function getListData()
{
	var clientContext = new SP.ClientContext.get_current();
	var web = clientContext.get_web();
	var userInfoList = web.get_lists().getByTitle('user_list')
	var camlQuery = new SP.CamlQuery();
	var caml = '';
	caml += '<View>';
	caml += '	<Query>';
	caml += '		<OrderBy>';
	caml += '			<FieldRef Name="Title" Ascending="False" />';
	caml += '		</OrderBy>';
	caml += '	</Query>';
	caml += '</View>';
	camlQuery.set_viewXml(caml);
	collListItem = userInfoList.getItems(camlQuery);
	clientContext.load(collListItem);
	var onQuerySucceeded=function(sender, args)
	{
		var oitem;
		var s='';
		var n=0;
		var len=collListItem.get_count();
		var results=[];
		while(n < len)
		{
			oitem = collListItem.itemAt(n);
			s+="Title:"+oitem.get_item("Title")+"<br></br>";
			n++;
		}
		$("#output").append(s);
	}
	var onQueryFailed=function(sender, args)
	{
		alert("Failed getting data.")
	}
	clientContext.executeQueryAsync
        (
        Function.createDelegate(this, onQuerySucceeded),
        Function.createDelegate(this, onQueryFailed)
        );
}

Output of Title column from a SharePoint 2010 list.

When an app or game is written we "expect" the user to precisely press the proper key or key combination at a time to execute programmatic actions. However, most of us have ten fingers and we use more than one finger to press more than one button on the keyboard. The expected program reaction from multiple fingered keyboard input might not occur because you have another function executing when you expect just one at a time.

Key Combinations
Imagine you are using the keyboard to play a game. The RIGHT arrow key is for moving your character right, the LEFT arrow key is for moving your character LEFT.
Ok, the action in this game is heating up, you are pressing LEFT to avoid the lasers shooting at you. You successfully dodged the lasers, now you press RIGHT to move in and attack...but in the heat of battle, your other finger is still on the LEFT button. What happens now is your character most likely gets stuck, because both movement keys are pressed telling the character to go in opposite directions!

In some cases allowing multiple key presses is how you want the app to react. For example you want the user to press both UP and RIGHT keys to move the characters in a diagonal direction. When to allow this and when not can be different among all of the control buttons. It becomes messy having to write "If" and "switch" statements to make the KeyboardEvent listeners work according to the different controls needed.

Key Sequences
If you love video games cheats or the easter eggs developers sometimes place in apps you'll remember to access them, you will usually enter in a sequence of key presses. If you entered the sequence successfully you would have access to cool game cheats or some special developer mode of an application.

KeyManager
For the above reasons I've written a KeyManager class to add key control that allows individual keys/keycombos the option to cancel out the any previous key/keycombo that are pressed down...and when key/keycombos are released, whatever key/keycombo that are still pressed will be active again. And for detecting key press sequences the KeyManager class will allow also.

This is a basic example using KeyManager. The "addKey" method is for adding key press combos and the "addKeySequence" is for obviously adding
key press sequences.

In the working flash example, you can click "singular combos" checkbox to false, to see the problem described previously about the character getting stuck when pressing RIGHT and LEFT key at the same time. When you set the checkbox back to true you will notice how each new key press overrides any others that are still down. This results in responsive execution if a user has a habit of holding down other keys while pressing new ones..

Also in the working sample above if you enter in the proper key sequence you will be rewarded with an "Easter Egg" to view the source and FLA.

Example usage:

import net.keithhair.KeyManager;

var keyManager:KeyManager;
keyManager=new KeyManager(stage);
keyManager.addKey(["right"], goRight,stopRight,"control1");
keyManager.addKey(["left"], goLeft,stopLeft,"control2");
keyManager.addKey(["up"], goUp,stopUp,"control3");
keyManager.addKey(["down"], goDown,stopDown,"control4");
keyManager.addKey(["shift","w","t"], toggleWindow);
keyManager.addKeySequence(["up","up","down","down","left","right","left","right"],openEasterEgg);