Angular component naming limitations - 'selector [your component name] is invalid'

Question

In Angular 6 (6.0.7) I'm trying to generate a component via the CLI. I type in ng g c t1-2-3-user and get the error message Selector (app-t1-2-3-user) is invalid.

Is there something inherently not allowed in this name? I've already created a parent module called t1-myModule via ng g module t1-myModule and it was created successfully. Within that module is where I'm trying to generate this component.

I've tried creating a different name like ng g c t1-testComponent and it works fine - so the CLI doesn't appear to be broken. Something about naming a component t1-2-3-user in my setup is not liked by Angular.

EDIT: after further testing, it appears Angular doesn't like the first character after a dash - to be a number. Possibly a similar limitation as in JavaScript variables. I assume since it gets compiled into JavaScript? Can anyone elaborate on/confirm this component naming constraint?

Answer 1

As per W3C standards selector should qualify below set of things

In CSS, identifiers (including element names, classes, and IDs in selectors) can contain

1. only the characters [a-zA-Z0-9] and ISO 10646 characters U+00A0 and higher, plus the hyphen (-) and the underscore (_);
2. they cannot start with a digit, two hyphens, or a hyphen followed by a digit
3. Identifiers can also contain escaped characters and any ISO 10646 character as a numeric code (see next item). For instance, the identifier "B&W?" may be written as "B\&W\?" or "B\26 W\3F".

So Angular is following the W3C convention for selector name. I was expected to see similar thing baked in inside code somewhere. After digging into CLI code It turns out that angular uses regex (/^[a-zA-Z][.0-9a-zA-Z]*(:?-[a-zA-Z][.0-9a-zA-Z]*)*$/) to validate selector name before creating files.

So while running ng generate component component-name command it calls @angular/schematics for component command and pass the component name parameter to it. While executing command with set of instruction it fires below line to validate selector.

validateHtmlSelector(options.selector);

validation.ts

export const htmlSelectorRe = /^[a-zA-Z][.0-9a-zA-Z]*(:?-[a-zA-Z][.0-9a-zA-Z]*)*$/;
export function validateHtmlSelector(selector: string): void {
  if (selector && !htmlSelectorRe.test(selector)) {
    throw new SchematicsException(tags.oneLine`Selector (${selector})
        is invalid.`);
  }
}