How does PrimeNG use classes to display icons instead of HTML tags?

Question

I was reading through the GitHub project and noticed that icons extend from a BaseIcon class, which in turn extends from a BaseComponent. From what I saw, you can use the selector, for example, <AngleUpIcon>, to display the SVG of that icon. However, I would like to understand how PrimeNG manages to display icons using classes, for example:

<i class="pi pi-user" style="font-size: 2.5rem"></i>

Find a clear explanation of how PrimeNG achieves the functionality of displaying icons using classes instead of HTML tags, possibly through custom components or other mechanisms.

Answer 1

https://github.com/primefaces/primeicons/blob/master/primeicons.css — this is the explanation you're looking for.

Basically, they use PrimeIcons, which are organized as a font. .pi CSS class specifies that it should use this font, and adds some rendering hints:

.pi {
    font-family: 'primeicons';
    speak: none;
    font-style: normal;
    font-weight: normal;
    font-variant: normal;
    text-transform: none;
    line-height: 1;
    display: inline-block;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

While the specific class, e.g. .pi-user, simply specifies which symbol to render before your empty element:

.pi-user:before {
    content: "\e939";
}

This char code corresponds to the necessary icon in the font.

Obviously, having the whole icon set as a single file reduces the number of HTTP requests, which is the primary reason to organize it that way.