diff --git a/.changeset/plenty-carrots-confess.md b/.changeset/plenty-carrots-confess.md
new file mode 100644
index 0000000000..1387000cf6
--- /dev/null
+++ b/.changeset/plenty-carrots-confess.md
@@ -0,0 +1,5 @@
+---
+'@urql/core': patch
+---
+
+Remove `for-of` syntax from `@urql/core` helpers for JSC memory reduction.
diff --git a/packages/core/src/client.ts b/packages/core/src/client.ts
index 0cf9b74fc3..6f196003b9 100755
--- a/packages/core/src/client.ts
+++ b/packages/core/src/client.ts
@@ -649,7 +649,8 @@ export const Client: new (opts: ClientOptions) => Client = function Client(
             } else {
               // If the current result has queued up an operation of the same
               // key, then `stale` refers to it
-              for (const operation of queue) {
+              for (let i = 0; i < queue.length; i++) {
+                const operation = queue[i];
                 if (operation.key === result.operation.key) {
                   dispatched.delete(operation.key);
                   break;
diff --git a/packages/core/src/gql.ts b/packages/core/src/gql.ts
index 1254e74a6c..d5505a31fd 100644
--- a/packages/core/src/gql.ts
+++ b/packages/core/src/gql.ts
@@ -78,8 +78,9 @@ function gql(parts: string | TemplateStringsArray /* arguments */) {
   }
 
   source.unshift(keyDocument(body));
-  for (const document of source) {
-    for (const definition of document.definitions) {
+  for (let i = 0; i < source.length; i++) {
+    for (let j = 0; j < source[i].definitions.length; j++) {
+      const definition = source[i].definitions[j];
       if (definition.kind === Kind.FRAGMENT_DEFINITION) {
         const name = definition.name.value;
         const value = stringifyDocument(definition);
diff --git a/packages/core/src/utils/collectTypenames.ts b/packages/core/src/utils/collectTypenames.ts
index 0b4e3cbb07..a9d6091551 100755
--- a/packages/core/src/utils/collectTypenames.ts
+++ b/packages/core/src/utils/collectTypenames.ts
@@ -5,7 +5,9 @@ interface EntityLike {
 
 const collectTypes = (obj: EntityLike | EntityLike[], types: Set<string>) => {
   if (Array.isArray(obj)) {
-    for (const item of obj) collectTypes(item, types);
+    for (let i = 0, l = obj.length; i < l; i++) {
+      collectTypes(obj[i], types);
+    }
   } else if (typeof obj === 'object' && obj !== null) {
     for (const key in obj) {
       if (key === '__typename' && typeof obj[key] === 'string') {
diff --git a/packages/core/src/utils/error.ts b/packages/core/src/utils/error.ts
index eeae84df6e..102f2f45f8 100644
--- a/packages/core/src/utils/error.ts
+++ b/packages/core/src/utils/error.ts
@@ -8,9 +8,9 @@ const generateErrorMessage = (
   let error = '';
   if (networkErr) return `[Network] ${networkErr.message}`;
   if (graphQlErrs) {
-    for (const err of graphQlErrs) {
+    for (let i = 0, l = graphQlErrs.length; i < l; i++) {
       if (error) error += '\n';
-      error += `[GraphQL] ${err.message}`;
+      error += `[GraphQL] ${graphQlErrs[i].message}`;
     }
   }
   return error;
diff --git a/packages/core/src/utils/formatDocument.ts b/packages/core/src/utils/formatDocument.ts
index 3042f28187..da04dd4071 100644
--- a/packages/core/src/utils/formatDocument.ts
+++ b/packages/core/src/utils/formatDocument.ts
@@ -16,8 +16,8 @@ const formatNode = <
 ): FormattedNode<T> => {
   if ('definitions' in node) {
     const definitions: FormattedNode<DefinitionNode>[] = [];
-    for (const definition of node.definitions) {
-      const newDefinition = formatNode(definition);
+    for (let i = 0, l = node.definitions.length; i < l; i++) {
+      const newDefinition = formatNode(node.definitions[i]);
       definitions.push(newDefinition);
     }
 
@@ -27,7 +27,8 @@ const formatNode = <
   if ('directives' in node && node.directives && node.directives.length) {
     const directives: DirectiveNode[] = [];
     const _directives = {};
-    for (const directive of node.directives) {
+    for (let i = 0, l = node.directives.length; i < l; i++) {
+      const directive = node.directives[i];
       let name = directive.name.value;
       if (name[0] !== '_') {
         directives.push(directive);
@@ -43,7 +44,8 @@ const formatNode = <
     const selections: FormattedNode<SelectionNode>[] = [];
     let hasTypename = node.kind === Kind.OPERATION_DEFINITION;
     if (node.selectionSet) {
-      for (const selection of node.selectionSet.selections || []) {
+      for (let i = 0, l = node.selectionSet.selections.length; i < l; i++) {
+        const selection = node.selectionSet.selections[i];
         hasTypename =
           hasTypename ||
           (selection.kind === Kind.FIELD &&
diff --git a/packages/core/src/utils/request.ts b/packages/core/src/utils/request.ts
index f0675c82b1..41af16f3dc 100644
--- a/packages/core/src/utils/request.ts
+++ b/packages/core/src/utils/request.ts
@@ -180,7 +180,8 @@ export const createRequest = <
  * @returns the operation's name contained within the document, or `undefined`
  */
 export const getOperationName = (query: DocumentNode): string | undefined => {
-  for (const node of query.definitions) {
+  for (let i = 0, l = query.definitions.length; i < l; i++) {
+    const node = query.definitions[i];
     if (node.kind === Kind.OPERATION_DEFINITION) {
       return node.name ? node.name.value : undefined;
     }
@@ -192,7 +193,8 @@ export const getOperationName = (query: DocumentNode): string | undefined => {
  * @returns the operation's type contained within the document, or `undefined`
  */
 export const getOperationType = (query: DocumentNode): string | undefined => {
-  for (const node of query.definitions) {
+  for (let i = 0, l = query.definitions.length; i < l; i++) {
+    const node = query.definitions[i];
     if (node.kind === Kind.OPERATION_DEFINITION) {
       return node.operation;
     }
diff --git a/packages/core/src/utils/result.ts b/packages/core/src/utils/result.ts
index 119081ccdd..81c04d4b8c 100644
--- a/packages/core/src/utils/result.ts
+++ b/packages/core/src/utils/result.ts
@@ -53,13 +53,18 @@ export const makeResult = (
 
 const deepMerge = (target: any, source: any): any => {
   if (typeof target === 'object' && target != null) {
+    if (Array.isArray(target)) {
+      target = [...target];
+      for (let i = 0, l = source.length; i < l; i++)
+        target[i] = deepMerge(target[i], source[i]);
+    }
     if (
       !target.constructor ||
       target.constructor === Object ||
       Array.isArray(target)
     ) {
-      target = Array.isArray(target) ? [...target] : { ...target };
-      for (const key of Object.keys(source))
+      target = { ...target };
+      for (const key in source)
         target[key] = deepMerge(target[key], source[key]);
       return target;
     }
@@ -108,7 +113,8 @@ export const mergeResultPatch = (
 
   const withData = { data: prevResult.data };
   if (incremental) {
-    for (const patch of incremental) {
+    for (let i = 0, l = incremental.length; i < l; i++) {
+      const patch = incremental[i];
       if (Array.isArray(patch.errors)) {
         errors.push(...(patch.errors as any));
       }
diff --git a/packages/core/src/utils/variables.ts b/packages/core/src/utils/variables.ts
index fb3cf50f17..360067365c 100644
--- a/packages/core/src/utils/variables.ts
+++ b/packages/core/src/utils/variables.ts
@@ -12,9 +12,9 @@ const stringify = (x: any, includeFiles: boolean): string => {
     return stringify(x.toJSON(), includeFiles);
   } else if (Array.isArray(x)) {
     let out = '[';
-    for (const value of x) {
+    for (let i = 0, l = x.length; i < l; i++) {
       if (out.length > 1) out += ',';
-      out += stringify(value, includeFiles) || 'null';
+      out += stringify(x[i], includeFiles) || 'null';
     }
     out += ']';
     return out;
@@ -39,11 +39,11 @@ const stringify = (x: any, includeFiles: boolean): string => {
 
   seen.add(x);
   let out = '{';
-  for (const key of keys) {
-    const value = stringify(x[key], includeFiles);
+  for (let i = 0, l = keys.length; i < l; i++) {
+    const value = stringify(x[keys[i]], includeFiles);
     if (value) {
       if (out.length > 1) out += ',';
-      out += stringify(key, includeFiles) + ':' + value;
+      out += stringify(keys[i], includeFiles) + ':' + value;
     }
   }
 
@@ -62,7 +62,7 @@ const extract = (map: FileMap, path: string, x: any): void => {
     map.set(path, x as File | Blob);
   } else {
     seen.add(x);
-    for (const key of Object.keys(x)) extract(map, `${path}.${key}`, x[key]);
+    for (const key in x) extract(map, `${path}.${key}`, x[key]);
   }
 };