String formatting & interpolation

In Jess, interpolation is the canonical way to build strings. It reads clearly and does not depend on positional format tokens:

$name: world;
.a {
  content: "hello ${name}";   // -> "hello world"
}

The %() compatibility alias

Jess also accepts Less's printf-style %(...) format function for compatibility. It is a thin alias that lowers to an ordinary string-format call — not a special syntactic form:

.a { x: %("rgb(%d, %d, %d)", 255, 0, 0); }  // -> "rgb(255, 0, 0)"
.b { x: %("hello %s", "world"); }            // -> "hello world"

Tokens: %d/%s/%a insert the next argument (%s strips quotes); an uppercase token URL-encodes; %% emits a literal %. Because arguments insert as their verbatim value, %("%s", #123) yields "#123".

Prefer interpolation for new Jess code; reach for %() mainly when porting existing Less.

note

%(...) is the compatibility alias for the public string-format function (named string-format rather than format to avoid colliding with CSS format()). You can call it directly:

.a { x: string-format("rgb(%d, %d, %d)", 255, 0, 0); }  // -> "rgb(255, 0, 0)"

See also the Less String Formatting page.