Function parseOnTrigger

packages/compiler/src/render3/r3_deferred_triggers.ts:128–167

(
  {expression, sourceSpan}: html.BlockParameter,
  bindingParser: BindingParser,
  triggers: t.DeferredBlockTriggers,
  errors: ParseError[],
  placeholder: t.DeferredBlockPlaceholder | null,
)

/** Parses an `on` trigger */
export function parseOnTrigger(
  {expression, sourceSpan}: html.BlockParameter,
  bindingParser: BindingParser,
  triggers: t.DeferredBlockTriggers,
  errors: ParseError[],
  placeholder: t.DeferredBlockPlaceholder | null,
): void {
  const onIndex = expression.indexOf('on');
  const onSourceSpan = new ParseSourceSpan(
    sourceSpan.start.moveBy(onIndex),
    sourceSpan.start.moveBy(onIndex + 'on'.length),
  );
  const prefetchSpan = getPrefetchSpan(expression, sourceSpan);
  const hydrateSpan = getHydrateSpan(expression, sourceSpan);

  // This is here just to be safe, we shouldn't enter this function
  // in the first place if a block doesn't have the "on" keyword.
  if (onIndex === -1) {
    errors.push(new ParseError(sourceSpan, `Could not find "on" keyword in expression`));
  } else {
    const start = getTriggerParametersStart(expression, onIndex + 1);
    const isHydrationTrigger = expression.startsWith('hydrate');
    const parser = new OnTriggerParser(
      expression,
      bindingParser,
      start,
      sourceSpan,
      triggers,
      errors,
      isHydrationTrigger
        ? validateHydrateReferenceBasedTrigger
        : validatePlainReferenceBasedTrigger,
      isHydrationTrigger,
      prefetchSpan,
      onSourceSpan,
      hydrateSpan,
    );
    parser.parse();
  }
}

function getPrefetchSpan(expression: string, sourceSpan: ParseSourceSpan) {
  if (!expression.startsWith('prefetch')) {