I'm starting to learn some javascript and understand that dashes are not permitted when naming identifiers. However, in CSS it's common to use a dash for IDs and classes.
Does using a dash in CSS interfere with javascript interaction somehow? For instance if I were to use getElementByID("css-dash-name"). I've tried a few examples using getElementByID with dashes as a name for a div ID and it worked, but I'm not sure if that's the case in all other contexts.
Having dashes and underscores in the ID (or class name if you select by that) that won't have any negative effect, it's safe to use them. You just can't do something like:
var some-element = document.getElementByID('css-dash-name');
The above example is going to error out because there is a dash in the variable you're assigning the element to.
The following would be fine though since the variable doesn't contain a dash:
var someElement = document.getElementByID('css-dash-name');
That naming limitation only exists for the javascript variables themselves.
It's only in the cases where you can access the elements as properties that it makes a difference. For example form fields:
<form>
<input type="text" name="go-figure" />
<input type="button" value="Eat me!" onclick="...">
</form>
In the onclick event you can't access the text box as a property, as the dash is interpreted as minus in Javascript:
onclick="this.form.go-figure.value='Ouch!';"
But you can still access it using a string:
onclick="this.form['go-figure'].value='Ouch!';"
Whenever you have to address a CSS property as a JavaScript variable name, CamelCase is the official way to go.
element.style.backgroundColor = "#FFFFFF";
You will never be in the situation to have to address a element's ID as a variable name. It will always be in a string, so
document.getElementById("my-id");
will always work.
Using Hypen (or dash) is OK
I too is currently studying JavaScript, and as far as I read David Flanagan's book (JavaScript: The Definitive Guide, 5th Edition) — I suggest you read it. It doesn't warn me anything about the use of hypen or dash (-) in IDs and Classes (even the Name attribute) in an HTML document.
Just as what Parrots already said, hypens are not allowed in variables, because the JavaScript interpreter will treat it as a minus and/or a negative sign; but to use it on strings, is pretty much ok.
Like what Parrots and Guffa said, you can use the following ...
"" (double quotation marks or double quotes)
to tell the JavaScript interpreter that your are declaring strings (the id/class/name of your elements for instance).
Use Hyphen (or dash) — for 'Consistency'
@KP, that would be ok if he is using HTML 4.1 or earlier, but if he is using any versions of XHTML (.e.g., XHTML 1.0), then that cannot be possible, because XHTML syntax prohibits uppercase (except the !DOCTYPE, which is the only thing that needs to declared in uppercase).
@Choy, if you're using HTML 4.1 or earlier, going to either camelCase or PascalCase will not be a problem. Although, for consistency's sake as to how CSS use separators (it uses hypen or dash), I suggest following its rule. It will be much more convinient for you to code your HTML and CSS alike. And moreoever, you don't even have to worry if you're using XHTML or HTML.
IDs are allowed to contain hyphens:
- ID and NAME tokens must begin with a letter ([A-Za-z]) and may be followed by any number of letters, digits ([0-9]), hyphens ("-"), underscores ("_"), colons (":"), and periods (".").
And there is no restriction when using IDs in JavaScript except if you want to refer to elements in the global scope. There you need to use:
window['css-dash-name']
Other answers are correct as far as where you can and can't use hyphens, however at the root of the question, you should consider the idea of not using dashes/hyphens in your variable/class/ID names altogether. It's not standard practice, even if it does work and requires careful coding to make use of it.
Consider using either PascalCase (all words begin in capital) or camelCase (first word begins in lowercase, following words being in uppercase). These are the two most common, accepted naming conventions.
Different resources will recommend different choices between the two (with the exception of JavaScript which is pretty much always recommended camelCase). In the end as long as you are consistent in your approach, this is the most important part. Using camel or Pascal case will ensure you don't have to worry about special accessors or brackets in your code.
For JavaScript conventions, try this question/discussion:
Here's another great discussion of conventions for CSS, Html elements, etc:
What's the best way to name IDs and classes in CSS and HTML?
It would cause an error in this case:
const fontSize = element.style.font-size;
Because including a hyphen prevents the property from being accessed via the dot operator. The JavaScript parser would see the hyphen as a subtraction operator. Correct way would be:
const fontSize = element.style['font-size']
No, this won't cause an issue. You're accessing the ID as a string (it's enclosed in quotes), so the dash poses no problem. However, I would suggest not using document.getElementById("css-dash-name"), and instead using jQuery, so you can do:
$("#css-dash-name");
Which is much clearer. the jQuery documentation is also quite good. It's a web developers best friend.
