diff --git a/NativeScript/runtime/js/blob-url.js b/NativeScript/runtime/js/blob-url.js
index f6ce429b..94c3fcf4 100644
--- a/NativeScript/runtime/js/blob-url.js
+++ b/NativeScript/runtime/js/blob-url.js
@@ -1,4 +1,6 @@
 const {
+    ArrayPrototypePush,
+    FunctionPrototypeCall,
     Map,
     MapPrototypeDelete,
     MapPrototypeGet,
@@ -39,35 +41,89 @@ InternalAccessor.getData = function (url) {
     return MapPrototypeGet(BLOB_STORE, url);
 };
 URL.InternalAccessor = InternalAccessor;
+
+// Pushes the params object's serialization onto its URL and records it as the
+// query string the params object is in sync with.
+function writeBack(params) {
+    const url = params._url;
+    url.search = params.toString();
+    url._searchParamsSource = url.search;
+}
+
+// Brings `params` back in line with its URL's current query string by mutating
+// it in place: url.searchParams is a same-object accessor, so the one params
+// object handed out for a URL has to survive every reparse of that URL. Only
+// the raw methods captured at construction are used here — the public ones are
+// wrapped to write back into the URL, which would clobber the very string being
+// applied.
+function resync(params) {
+    const url = params._url;
+    const search = url.search;
+    if (url._searchParamsSource === search) {
+        return;
+    }
+    const names = [];
+    FunctionPrototypeCall(params._forEach, params, function (value, name) {
+        ArrayPrototypePush(names, name);
+    });
+    for (let i = 0; i < names.length; i++) {
+        FunctionPrototypeCall(params._delete, params, names[i]);
+    }
+    const parsed = new URLSearchParamsCtor(search);
+    FunctionPrototypeCall(params._forEach, parsed, function (value, name) {
+        FunctionPrototypeCall(params._append, params, name, value);
+    });
+    url._searchParamsSource = search;
+}
+
 ObjectDefineProperty(URL.prototype, 'searchParams', {
     get() {
         if (this._searchParams == null) {
-            this._searchParams = new URLSearchParamsCtor(this.search);
-            ObjectDefineProperty(this._searchParams, '_url', {
+            const params = new URLSearchParamsCtor(this.search);
+            ObjectDefineProperty(this, '_searchParams', {
+                enumerable: false,
+                writable: true,
+                configurable: true,
+                value: params,
+            });
+            ObjectDefineProperty(this, '_searchParamsSource', {
+                enumerable: false,
+                writable: true,
+                configurable: true,
+                value: this.search,
+            });
+            ObjectDefineProperty(params, '_url', {
                 enumerable: false,
                 writable: false,
                 value: this,
             });
-            this._searchParams._append = this._searchParams.append;
-            this._searchParams.append = function (name, value) {
+            params._forEach = params.forEach;
+            params._append = params.append;
+            params.append = function (name, value) {
+                resync(this);
                 this._append(name, value);
-                this._url.search = this.toString();
+                writeBack(this);
             };
-            this._searchParams._delete = this._searchParams.delete;
-            this._searchParams.delete = function (name) {
+            params._delete = params.delete;
+            params.delete = function (name) {
+                resync(this);
                 this._delete(name);
-                this._url.search = this.toString();
+                writeBack(this);
             };
-            this._searchParams._set = this._searchParams.set;
-            this._searchParams.set = function (name, value) {
+            params._set = params.set;
+            params.set = function (name, value) {
+                resync(this);
                 this._set(name, value);
-                this._url.search = this.toString();
+                writeBack(this);
             };
-            this._searchParams._sort = this._searchParams.sort;
-            this._searchParams.sort = function () {
+            params._sort = params.sort;
+            params.sort = function () {
+                resync(this);
                 this._sort();
-                this._url.search = this.toString();
+                writeBack(this);
             };
+        } else {
+            resync(this._searchParams);
         }
         return this._searchParams;
     },
diff --git a/TestRunner/app/tests/ErrorEventsTests.js b/TestRunner/app/tests/ErrorEventsTests.js
index 4a3dc6ab..dc312297 100644
--- a/TestRunner/app/tests/ErrorEventsTests.js
+++ b/TestRunner/app/tests/ErrorEventsTests.js
@@ -67,8 +67,11 @@ describe("WHATWG error events", function () {
         expect(received.error).toBe(err);
         expect(received.message).toBe("x");
         // preventDefault() in the listener must suppress the __onUncaughtError shim.
+        // The hook is process-wide, so assert on this error rather than on the
+        // spy being empty: async failures from earlier suites can still drain
+        // into it while this test waits.
         afterQuietTurns(function () {
-            expect(uncaught.length).toBe(0);
+            expect(uncaught.indexOf(err)).toBe(-1);
             done();
         });
     });
@@ -154,7 +157,7 @@ describe("WHATWG error events", function () {
             expect(typeof received.reason.stackTrace).toBe("string");
             expect(received.reason.stackTrace.length).toBeGreaterThan(0);
             afterQuietTurns(function () {
-                expect(uncaught.length).toBe(0);
+                expect(uncaught.indexOf(reason)).toBe(-1);
                 done();
             });
         });
@@ -326,7 +329,7 @@ describe("WHATWG error events", function () {
         expect(received).not.toBeNull();
         expect(received.error).toBe(err);
         afterQuietTurns(function () {
-            expect(uncaught.length).toBe(0);
+            expect(uncaught.indexOf(err)).toBe(-1);
             done();
         });
     });
diff --git a/TestRunner/app/tests/UrlSearchParamsTests.js b/TestRunner/app/tests/UrlSearchParamsTests.js
new file mode 100644
index 00000000..2e8d6e4f
--- /dev/null
+++ b/TestRunner/app/tests/UrlSearchParamsTests.js
@@ -0,0 +1,149 @@
+describe("URL.searchParams caching", function () {
+  it("returns the same object across reads", function () {
+    const url = new URL("https://example.com/?a=1");
+    expect(url.searchParams).toBe(url.searchParams);
+  });
+
+  it("parses the query string on the first read", function () {
+    const url = new URL("https://example.com/?a=1&b=2&b=3");
+    const sp = url.searchParams;
+    expect(sp.get("a")).toBe("1");
+    expect(sp.getAll("b")).toEqual(["2", "3"]);
+    expect(sp.size).toBe(3);
+  });
+
+  it("keeps the same object after assigning to search", function () {
+    const url = new URL("https://example.com/?a=1");
+    const sp = url.searchParams;
+    url.search = "?x=1";
+    expect(url.searchParams).toBe(sp);
+  });
+
+  it("refreshes after assigning to search", function () {
+    const url = new URL("https://example.com/?a=1");
+    const sp = url.searchParams;
+    expect(sp.get("a")).toBe("1");
+
+    url.search = "?b=2&c=3";
+
+    expect(url.searchParams.get("a")).toBe(null);
+    expect(url.searchParams.get("b")).toBe("2");
+    expect(url.searchParams.get("c")).toBe("3");
+    expect(url.searchParams.size).toBe(2);
+    expect(sp.get("b")).toBe("2");
+  });
+
+  it("refreshes after assigning to href", function () {
+    const url = new URL("https://example.com/?a=1");
+    const sp = url.searchParams;
+    expect(sp.get("a")).toBe("1");
+
+    url.href = "https://example.com/other?q=hello&lang=en";
+
+    expect(url.searchParams).toBe(sp);
+    expect(url.searchParams.get("a")).toBe(null);
+    expect(url.searchParams.get("q")).toBe("hello");
+    expect(url.searchParams.get("lang")).toBe("en");
+  });
+
+  it("refreshes to empty when the query is cleared", function () {
+    const url = new URL("https://example.com/?a=1&b=2");
+    const sp = url.searchParams;
+    expect(sp.size).toBe(2);
+
+    url.search = "";
+
+    expect(url.searchParams).toBe(sp);
+    expect(url.searchParams.size).toBe(0);
+    expect(url.searchParams.toString()).toBe("");
+  });
+
+  it("preserves duplicate keys when refreshing", function () {
+    const url = new URL("https://example.com/?a=1");
+    const sp = url.searchParams;
+
+    url.search = "?a=1&a=2&a=3";
+
+    expect(url.searchParams.getAll("a")).toEqual(["1", "2", "3"]);
+    expect(sp.getAll("a")).toEqual(["1", "2", "3"]);
+  });
+
+  it("writes mutations back to the url", function () {
+    const url = new URL("https://example.com/?a=1");
+    const sp = url.searchParams;
+
+    sp.set("a", "9");
+    expect(url.search).toBe("?a=9");
+
+    sp.append("b", "2");
+    expect(url.search).toBe("?a=9&b=2");
+    expect(url.href).toBe("https://example.com/?a=9&b=2");
+
+    sp.delete("a");
+    expect(url.search).toBe("?b=2");
+
+    sp.append("a", "0");
+    sp.sort();
+    expect(url.search).toBe("?a=0&b=2");
+  });
+
+  it("does not drop state on the read following a mutation", function () {
+    const url = new URL("https://example.com/?a=1");
+    const sp = url.searchParams;
+
+    sp.append("b", "2");
+    sp.append("b", "3");
+
+    const spAfter = url.searchParams;
+    expect(spAfter).toBe(sp);
+    expect(spAfter.getAll("b")).toEqual(["2", "3"]);
+    expect(spAfter.get("a")).toBe("1");
+    expect(spAfter.size).toBe(3);
+  });
+
+  it("interleaves mutations and direct assignments", function () {
+    const url = new URL("https://example.com/?a=1");
+    const sp = url.searchParams;
+
+    sp.set("a", "2");
+    url.search = "?b=1";
+
+    expect(url.searchParams.get("a")).toBe(null);
+    expect(url.searchParams.get("b")).toBe("1");
+
+    sp.set("c", "3");
+    expect(url.search).toBe("?b=1&c=3");
+    expect(url.searchParams.get("c")).toBe("3");
+  });
+
+  it("does not clobber a reassigned query when mutating a held reference", function () {
+    const url = new URL("https://example.com/?a=1");
+    const sp = url.searchParams;
+
+    url.search = "?b=1";
+    sp.set("c", "3");
+
+    expect(url.search).toBe("?b=1&c=3");
+    expect(sp.get("a")).toBe(null);
+  });
+
+  it("does not expose its cache as an enumerable property", function () {
+    const url = new URL("https://example.com/?a=1");
+    UNUSED(url.searchParams);
+    url.search = "?b=2";
+    UNUSED(url.searchParams);
+
+    const keys = Object.keys(url);
+    expect(keys.indexOf("_searchParams")).toBe(-1);
+    expect(keys.indexOf("_searchParamsSource")).toBe(-1);
+
+    const serialized = JSON.stringify(url);
+    expect(serialized.indexOf("_searchParams")).toBe(-1);
+    expect(serialized.indexOf("_searchParamsSource")).toBe(-1);
+
+    for (const key in url) {
+      expect(key).not.toBe("_searchParams");
+      expect(key).not.toBe("_searchParamsSource");
+    }
+  });
+});
diff --git a/TestRunner/app/tests/index.js b/TestRunner/app/tests/index.js
index 5ad49d89..e40a07c4 100644
--- a/TestRunner/app/tests/index.js
+++ b/TestRunner/app/tests/index.js
@@ -140,6 +140,7 @@ require("./Timers");
 
 require("./URL");
 require("./URLSearchParams");
+require("./UrlSearchParamsTests");
 require("./URLPattern");
 
 // HTTP ESM Loader tests