el/examples/browser-counter.el

// browser-counter.el — canonical browser DOM bridge example
//
// Compile with:  elc --target=js examples/browser-counter.el > counter.js
//
// Then include in an HTML page that has a <span id="count-display"> element.
// The page can call window.increment() from any onclick handler, e.g.:
//   <button onclick="increment()">+1</button>
//
// On load the display is initialised to "0".  Each call to increment()
// adds 1 and updates the display text.
//
// Demonstrates:
//   - dom_get_element   to locate a DOM node by id
//   - dom_set_text      to update visible text content
//   - dom_is_null       to guard against missing elements
//   - window_set        to expose an El function for inline event handlers
//   - state_set/get     for in-memory counter state (survives calls, resets
//                       on page reload — same semantics as the C state_* API)

fn init() -> Void {
    state_set("counter", 0)
    let display = dom_get_element("count-display")
    if !dom_is_null(display) {
        dom_set_text(display, "0")
    }
}

fn increment() -> Void {
    let current = str_to_int(state_get("counter"))
    let next = current + 1
    state_set("counter", next)
    let display = dom_get_element("count-display")
    if !dom_is_null(display) {
        dom_set_text(display, int_to_str(next))
    }
}

fn main() -> Void {
    init()
    window_set("increment", increment)
}