3 files changed, 29 insertions, 1 deletions
diff --git a/js/url_search_params.ts b/js/url_search_params.ts
index 85f4c0619..666ba6951 100644
--- a/js/url_search_params.ts
+++ b/js/url_search_params.ts
@@ -1,6 +1,6 @@
 // Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
 import { URL } from "./url";
-import { requiredArguments } from "./util";
+import { requiredArguments, isIterable } from "./util";
 
 export class URLSearchParams {
   private params: Array<[string, string]> = [];
@@ -17,6 +17,11 @@ export class URLSearchParams {
       return;
     }
 
+    if (isIterable(init)) {
+      this.params = [...init];
+      return;
+    }
+
     if (Object(init) !== init) {
       return;
     }
diff --git a/js/url_search_params_test.ts b/js/url_search_params_test.ts
index d37b55497..e270dd7ff 100644
--- a/js/url_search_params_test.ts
+++ b/js/url_search_params_test.ts
@@ -217,3 +217,13 @@ test(function urlSearchParamsDeletingAppendedMultiple(): void {
   params.delete("first");
   assertEquals(params.has("first"), false);
 });
+
+// ref: https://github.com/web-platform-tests/wpt/blob/master/url/urlsearchparams-constructor.any.js#L176-L182
+test(function urlSearchParamsCustomSymbolIterator(): void {
+  const params = new URLSearchParams();
+  params[Symbol.iterator] = function*(): IterableIterator<[string, string]> {
+    yield ["a", "b"];
+  };
+  const params1 = new URLSearchParams((params as unknown) as string[][]);
+  assertEquals(params1.get("a"), "b");
+});
diff --git a/js/util.ts b/js/util.ts
index a035d761a..da56465a2 100644
--- a/js/util.ts
+++ b/js/util.ts
@@ -122,6 +122,19 @@ export function isObject(o: unknown): o is object {
   return o != null && typeof o === "object";
 }
 
+// Returns whether o is iterable.
+export function isIterable<T, P extends keyof T, K extends T[P]>(
+  o: T
+): o is T & Iterable<[P, K]> {
+  // checks for null and undefined
+  if (o == null) {
+    return false;
+  }
+  return (
+    typeof ((o as unknown) as Iterable<[P, K]>)[Symbol.iterator] === "function"
+  );
+}
+
 // @internal
 export function requiredArguments(
   name: string,