Single vs Double quotes (' vs ")

The w3 org said:

By default, SGML requires that all attribute values be delimited using either double quotation marks (ASCII decimal 34) or single quotation marks (ASCII decimal 39). Single quote marks can be included within the attribute value when the value is delimited by double quote marks, and vice versa. Authors may also use numeric character references to represent double quotes (") and single quotes ('). For double quotes authors can also use the character entity reference ".

So... seems to be no difference. Only depends on your style.

I use " as a top-tier and ' as a second tier, as I imagine most people do. For example

<a href="#" onclick="alert('Clicked!');">Click Me!</a>

In that example, you must use both, it is unavoidable.

Single quotes vs Double quotes in PHP. (n.d.). Retrieved November 26, 2014, from http://www.scriptingok.com/tutorial/Single-quotes-vs-double-quotes-in-PHP

If it's all the same, perhaps using single-quotes is better since it doesn't require holding down the shift key. Fewer keystrokes == less chance of repetitive strain injury.

Actually, the best way is the way Google recommends. Double quotes: https://google.github.io/styleguide/htmlcssguide.xml?showone=HTML_Quotation_Marks#HTML_Quotation_Marks

See https://google.github.io/styleguide/htmlcssguide.xml?showone=HTML_Validity#HTML_Validity Quoted Advice from Google: "Using valid HTML is a measurable baseline quality attribute that contributes to learning about technical requirements and constraints, and that ensures proper HTML usage."

In HTML I don't believe it matters whether you use " or ', but it should be used consistently throughout the document.

My own usage prefers that attributes/html use ", whereas all javascript uses ' instead.

This makes it slightly easier, for me, to read and check. If your use makes more sense for you than mine would, there's no need for change. But, to me, your code would feel messy. It's personal is all.

Using double quotes for HTML

i.e.

<div class="colorFont"></div>

Using single quotes for JavaScript

i.e.

$('#container').addClass('colorFont');
$('<div class="colorFont2></div>');

I know LOTS of people wouldn't agree, but this is what I do and I really enjoy such a coding style: I actually don't use any quote in HTML unless it is absolutely necessary.

Example:

<form method=post action=#>
<fieldset>
<legend>Register here: </legend>
  <label for=account>Account: </label>
  <input id=account type=text name=account required><br>
  <label for=password>Password: </label>
  <input id=password type=password name=password required><br>
...

Double quotes are used only when there are spaces in the attribute values or whatever:

<form class="val1 val2 val3" method=post action=#>
  ...
</form>

I had an issue with Bootstrap where I had to use double quotes as single quotes didn't work.

class='row-fluid' made the last <span> fall below the other <span>s, rather than sitting nicely beside them on the far right. class="row-fluid" worked.

It makes no difference to the html but if you are generating html dynamically with another programming language then one way may be easier than another.

For example in Java the double quote is used to indicate the start and end of a String, so if you want to include a doublequote within the String you have to escape it with a backslash.

String s = "<a href=\"link\">a Link</a>"

You don't have such a problem with the single quote, therefore use of the single quote makes for more readable code in Java.

String s = "<a href='link'>a Link</a>"

Especially if you have to write html elements with many attributes.(Note I usually use a library such as jhtml to write html in Java, but not always practical to do so)

if you are writing asp.net then occasionally you have to use double quotes in Eval statements and single quotes for delimiting the values - this is mainly so that the C# inline code knows its using a string in the eval container rather than a character. Personally I'd only use one or the other as a standard and not mix them, it looks messy thats all.

Using " instead of ' when:

<input value="user"/> //Standard html
<input value="user's choice"/> //Need to use single quote
<input onclick="alert('hi')"/> //When giving string as parameter for javascript function

Using ' instead of " when:

<input value='"User"'/> //Need to use double quote
var html = "<input name='username'/>" //When assigning html content to a javascript variable

I'm newbie here but I use single quote mark only when I use double quote mark inside the first one. If I'm not clear I show You example:

<p align="center" title='One quote mark at the beginning so now I can
"cite".'> ... </p>

I hope I helped.

Lots of great insightful replies here! More than enough for anyone to make a clear and personal decision.

I would simply like to point out one thing that's always mattered to me. And take this with a grain of salt!

Double quotes apply to strings that have more than a single phase such as "one two" rather than single quotes for 'one' or 'two'. This can be traced as far back as C and C++.
(reference here or do your own online search).

And that's truly the difference.

With this principle (this different), parsing became possible such as "{{'a','b'},{'x','y'}} or "/[^\r\n]*[\r\n]" (which needed to be space independent because it's expressional) or more famously for HTML specific title = "Hello HTML!" or style = "font-family:arial; color:#FF0000;"

The funny thing here is that HTML (coming from XML itself) commonly adopted double quotes due to expressional features even if it is a single character (e.g. number) or single phase string.

As NibblyPig pointed out quite well and straightforward:
" as a top-tier and ' as a second tier since "'a string here'" is valid and expected by W3 standards (which is for the web) and will most likely never change.

And for consistency, double quotes is wisely used, but only fully correct by preference.

In PHP using double quotes causes a slight decrease in performance because variable names are evaluated, so in practice, I always use single quotes when writing code:

echo "This will print you the value of $this_variable!";
echo 'This will literally say $this_variable with no evaluation.';

So you can write this instead;

echo 'This will show ' . $this_variable . '!';

I believe Javascript functions similarly, so a very tiny improvement in performance, if that matters to you.

Additionally, if you look all the way down to HTML spec 2.0, all the tags listed here;

W3 HTML DTD Reference

(Use doublequotes.) Consistency is important no matter which you tend to use more often.

Double quotes are used for strings (i.e., "this is a string") and single quotes are used for a character (i.e., 'a', 'b' or 'c'). Depending on the programming language and context, you can get away with using double quotes for a character but not single quotes for a string.

HTML doesn't care about which one you use. However, if you're writing HTML inside a PHP script, you should stick with double quotes as you will need to escape them (i.e., \"whatever\") to avoid confusing yourself and PHP.