[FIX] components: make sure t-ref work with t-if/t-else

src/app/template_helpers.ts

@@ -141,6 +141,24 @@ function bind(ctx: any, fn: Function): Function {
   return boundFn;
 }
 
+type RefMap = { [key: string]: HTMLElement | null };
+type RefSetter = (el: HTMLElement | null) => void;
+
+function multiRefSetter(refs: RefMap, name: string): RefSetter {
+  let count = 0;
+  return (el) => {
+    if (el) {
+      count++;
+      if (count > 1) {
+        throw new Error("Cannot have 2 elements with same ref name at the same time");
+      }
+    }
+    if (count === 0 || el) {
+      refs[name] = el;
+    }
+  };
+}
+
 export const UTILS = {
   withDefault,
   zero: Symbol("zero"),
@@ -150,6 +168,7 @@ export const UTILS = {
   withKey,
   prepareList,
   setContextValue,
+  multiRefSetter,
   shallowEqual,
   toNumber,
   validateProps,