Function assertNoDuplicateDirectives

packages/core/src/render3/view/directives.ts:568–586

(directives: DirectiveDef<unknown>[])

}

function assertNoDuplicateDirectives(directives: DirectiveDef<unknown>[]): void {
  // The array needs at least two elements in order to have duplicates.
  if (directives.length < 2) {
    return;
  }

  const seenDirectives = new Set<DirectiveDef<unknown>>();

  for (const current of directives) {
    if (seenDirectives.has(current)) {
      throw new RuntimeError(
        RuntimeErrorCode.DUPLICATE_DIRECTIVE,
        `Directive ${current.type.name} matches multiple times on the same element. ` +
          `Directives can only match an element once.`,
      );
    }
    seenDirectives.add(current);
  }
}