diff --git a/dlls/jscript/engine.c b/dlls/jscript/engine.c
index eb15be43ace..52cdc88f80c 100644
--- a/dlls/jscript/engine.c
+++ b/dlls/jscript/engine.c
@@ -1698,13 +1698,11 @@ static HRESULT interp_typeofid(exec_ctx_t *ctx)
     DISPID id;
     HRESULT hres;
 
-    static const WCHAR undefinedW[] = {'u','n','d','e','f','i','n','e','d',0};
-
     TRACE("\n");
 
     obj = stack_pop_objid(ctx, &id);
     if(!obj)
-        return stack_push_string(ctx, undefinedW);
+        return stack_push(ctx, jsval_string(jsstr_undefined()));
 
     hres = disp_propget(ctx->script, obj, id, &v);
     IDispatch_Release(obj);
@@ -1735,7 +1733,7 @@ static HRESULT interp_typeofident(exec_ctx_t *ctx)
         return hres;
 
     if(exprval.type == EXPRVAL_INVALID) {
-        hres = stack_push_string(ctx, undefinedW);
+        hres = stack_push(ctx, jsval_string(jsstr_undefined()));
         exprval_release(&exprval);
         return hres;
     }
diff --git a/dlls/jscript/global.c b/dlls/jscript/global.c
index 0668e860d5b..739a8319f4d 100644
--- a/dlls/jscript/global.c
+++ b/dlls/jscript/global.c
@@ -286,14 +286,8 @@ static HRESULT JSGlobal_escape(script_ctx_t *ctx, vdisp_t *jsthis, WORD flags, u
     TRACE("\n");
 
     if(!argc) {
-        if(r) {
-            ret_str = jsstr_alloc(undefinedW);
-            if(!ret_str)
-                return E_OUTOFMEMORY;
-
-            *r = jsval_string(ret_str);
-        }
-
+        if(r)
+            *r = jsval_string(jsstr_undefined());
         return S_OK;
     }
 
@@ -640,13 +634,8 @@ static HRESULT JSGlobal_unescape(script_ctx_t *ctx, vdisp_t *jsthis, WORD flags,
     TRACE("\n");
 
     if(!argc) {
-        if(r) {
-            ret_str = jsstr_alloc(undefinedW);
-            if(!ret_str)
-                return E_OUTOFMEMORY;
-            *r = jsval_string(ret_str);
-        }
-
+        if(r)
+            *r = jsval_string(jsstr_undefined());
         return S_OK;
     }
 
@@ -781,14 +770,8 @@ static HRESULT JSGlobal_encodeURI(script_ctx_t *ctx, vdisp_t *jsthis, WORD flags
     TRACE("\n");
 
     if(!argc) {
-        if(r) {
-            ret = jsstr_alloc(undefinedW);
-            if(!ret)
-                return E_OUTOFMEMORY;
-
-            *r = jsval_string(ret);
-        }
-
+        if(r)
+            *r = jsval_string(jsstr_undefined());
         return S_OK;
     }
 
@@ -853,14 +836,8 @@ static HRESULT JSGlobal_decodeURI(script_ctx_t *ctx, vdisp_t *jsthis, WORD flags
     TRACE("\n");
 
     if(!argc) {
-        if(r) {
-            ret = jsstr_alloc(undefinedW);
-            if(!ret)
-                return E_OUTOFMEMORY;
-
-            *r = jsval_string(ret);
-        }
-
+        if(r)
+            *r = jsval_string(jsstr_undefined());
         return S_OK;
     }
 
@@ -944,14 +921,8 @@ static HRESULT JSGlobal_encodeURIComponent(script_ctx_t *ctx, vdisp_t *jsthis, W
     TRACE("\n");
 
     if(!argc) {
-        if(r) {
-            ret = jsstr_alloc(undefinedW);
-            if(!ret)
-                return E_OUTOFMEMORY;
-
-            *r = jsval_string(ret);
-        }
-
+        if(r)
+            *r = jsval_string(jsstr_undefined());
         return S_OK;
     }
 
@@ -1014,14 +985,8 @@ static HRESULT JSGlobal_decodeURIComponent(script_ctx_t *ctx, vdisp_t *jsthis, W
     TRACE("\n");
 
     if(!argc) {
-        if(r) {
-            ret = jsstr_alloc(undefinedW);
-            if(!ret)
-                return E_OUTOFMEMORY;
-
-            *r = jsval_string(ret);
-        }
-
+        if(r)
+            *r = jsval_string(jsstr_undefined());
         return S_OK;
     }
 
diff --git a/dlls/jscript/jsregexp.c b/dlls/jscript/jsregexp.c
index 43df35a1ca0..61e9a95a239 100644
--- a/dlls/jscript/jsregexp.c
+++ b/dlls/jscript/jsregexp.c
@@ -58,7 +58,6 @@ static const WCHAR idx7W[] = {'$','7',0};
 static const WCHAR idx8W[] = {'$','8',0};
 static const WCHAR idx9W[] = {'$','9',0};
 
-static const WCHAR undefinedW[] = {'u','n','d','e','f','i','n','e','d',0};
 static const WCHAR emptyW[] = {0};
 
 static inline RegExpInstance *regexp_from_vdisp(vdisp_t *vdisp)
@@ -487,21 +486,15 @@ static HRESULT RegExp_test(script_ctx_t *ctx, vdisp_t *jsthis, WORD flags, unsig
         jsval_t *r)
 {
     match_state_t *match;
-    heap_pool_t *mark;
     jsstr_t *undef_str;
+    heap_pool_t *mark;
     BOOL b;
     HRESULT hres;
 
     TRACE("\n");
 
-    if(!argc) {
-        undef_str = jsstr_alloc(undefinedW);
-        if(!undef_str)
-            return E_OUTOFMEMORY;
-    }
-
     mark = heap_pool_mark(&ctx->tmp_heap);
-    hres = run_exec(ctx, jsthis, argc ? argv[0] : jsval_string(undef_str), NULL, &match, &b);
+    hres = run_exec(ctx, jsthis, argc ? argv[0] : jsval_string(undef_str = jsstr_undefined()), NULL, &match, &b);
     heap_pool_clear(mark);
     if(!argc)
         jsstr_release(undef_str);
diff --git a/dlls/jscript/jsstr.c b/dlls/jscript/jsstr.c
index 59dfe9824c9..3fb50b4779f 100644
--- a/dlls/jscript/jsstr.c
+++ b/dlls/jscript/jsstr.c
@@ -88,7 +88,7 @@ jsstr_t *jsstr_concat(jsstr_t *str1, jsstr_t *str2)
     return ret;
 }
 
-static jsstr_t *empty_str, *nan_str;
+static jsstr_t *empty_str, *nan_str, *undefined_str;
 
 jsstr_t *jsstr_nan(void)
 {
@@ -100,14 +100,22 @@ jsstr_t *jsstr_empty(void)
     return jsstr_addref(empty_str);
 }
 
+jsstr_t *jsstr_undefined(void)
+{
+    return jsstr_addref(undefined_str);
+}
+
 BOOL init_strings(void)
 {
     static const WCHAR NaNW[] = { 'N','a','N',0 };
+    static const WCHAR undefinedW[] = {'u','n','d','e','f','i','n','e','d',0};
 
     if(!(empty_str = jsstr_alloc_buf(0)))
         return FALSE;
     if(!(nan_str = jsstr_alloc(NaNW)))
         return FALSE;
+    if(!(undefined_str = jsstr_alloc(undefinedW)))
+        return FALSE;
     return TRUE;
 }
 
@@ -115,4 +123,5 @@ void free_strings(void)
 {
     jsstr_release(empty_str);
     jsstr_release(nan_str);
+    jsstr_release(undefined_str);
 }
diff --git a/dlls/jscript/jsstr.h b/dlls/jscript/jsstr.h
index cbe68ef3437..c71cbea4293 100644
--- a/dlls/jscript/jsstr.h
+++ b/dlls/jscript/jsstr.h
@@ -76,6 +76,7 @@ jsstr_t *jsstr_concat(jsstr_t*,jsstr_t*) DECLSPEC_HIDDEN;
 
 jsstr_t *jsstr_nan(void) DECLSPEC_HIDDEN;
 jsstr_t *jsstr_empty(void) DECLSPEC_HIDDEN;
+jsstr_t *jsstr_undefined(void) DECLSPEC_HIDDEN;
 
 BOOL init_strings(void) DECLSPEC_HIDDEN;
 void free_strings(void) DECLSPEC_HIDDEN;
diff --git a/dlls/jscript/jsutils.c b/dlls/jscript/jsutils.c
index 5900d81d685..60260bba49a 100644
--- a/dlls/jscript/jsutils.c
+++ b/dlls/jscript/jsutils.c
@@ -738,15 +738,14 @@ HRESULT double_to_string(double n, jsstr_t **str)
 /* ECMA-262 3rd Edition    9.8 */
 HRESULT to_string(script_ctx_t *ctx, jsval_t val, jsstr_t **str)
 {
-    const WCHAR undefinedW[] = {'u','n','d','e','f','i','n','e','d',0};
     const WCHAR nullW[] = {'n','u','l','l',0};
     const WCHAR trueW[] = {'t','r','u','e',0};
     const WCHAR falseW[] = {'f','a','l','s','e',0};
 
     switch(jsval_type(val)) {
     case JSV_UNDEFINED:
-        *str = jsstr_alloc(undefinedW);
-        break;
+        *str = jsstr_undefined();
+        return S_OK;
     case JSV_NULL:
         *str = jsstr_alloc(nullW);
         break;
diff --git a/dlls/jscript/lex.c b/dlls/jscript/lex.c
index 8823a30b364..54c8fcf98ce 100644
--- a/dlls/jscript/lex.c
+++ b/dlls/jscript/lex.c
@@ -59,7 +59,6 @@ static const WCHAR throwW[] = {'t','h','r','o','w',0};
 static const WCHAR trueW[] = {'t','r','u','e',0};
 static const WCHAR tryW[] = {'t','r','y',0};
 static const WCHAR typeofW[] = {'t','y','p','e','o','f',0};
-static const WCHAR undefinedW[] = {'u','n','d','e','f','i','n','e','d',0};
 static const WCHAR varW[] = {'v','a','r',0};
 static const WCHAR voidW[] = {'v','o','i','d',0};
 static const WCHAR whileW[] = {'w','h','i','l','e',0};
diff --git a/dlls/jscript/string.c b/dlls/jscript/string.c
index 8f38621e6a1..2aa9e585c57 100644
--- a/dlls/jscript/string.c
+++ b/dlls/jscript/string.c
@@ -188,10 +188,7 @@ static HRESULT do_attributeless_tag_format(script_ctx_t *ctx, vdisp_t *jsthis, j
 static HRESULT do_attribute_tag_format(script_ctx_t *ctx, vdisp_t *jsthis, unsigned argc, jsval_t *argv, jsval_t *r,
         const WCHAR *tagname, const WCHAR *attrname)
 {
-    static const WCHAR undefinedW[] = {'u','n','d','e','f','i','n','e','d',0};
-
     jsstr_t *str, *attr_value = NULL;
-    unsigned attr_len;
     HRESULT hres;
 
     hres = get_string_val(ctx, jsthis, &str);
@@ -204,9 +201,8 @@ static HRESULT do_attribute_tag_format(script_ctx_t *ctx, vdisp_t *jsthis, unsig
             jsstr_release(str);
             return hres;
         }
-        attr_len = jsstr_length(attr_value);
     }else {
-        attr_len = sizeof(undefinedW)/sizeof(WCHAR)-1;
+        attr_value = jsstr_undefined();
     }
 
     if(r) {
@@ -214,7 +210,7 @@ static HRESULT do_attribute_tag_format(script_ctx_t *ctx, vdisp_t *jsthis, unsig
         unsigned tagname_len = strlenW(tagname);
         jsstr_t *ret;
 
-        ret = jsstr_alloc_buf(2*tagname_len + attrname_len + attr_len + jsstr_length(str) + 9);
+        ret = jsstr_alloc_buf(2*tagname_len + attrname_len + jsstr_length(attr_value) + jsstr_length(str) + 9);
         if(ret) {
             WCHAR *ptr = ret->str;
 
@@ -226,13 +222,7 @@ static HRESULT do_attribute_tag_format(script_ctx_t *ctx, vdisp_t *jsthis, unsig
             ptr += attrname_len;
             *ptr++ = '=';
             *ptr++ = '"';
-
-            if(attr_value)
-                jsstr_flush(attr_value, ptr);
-            else
-                memcpy(ptr, undefinedW, attr_len*sizeof(WCHAR));
-            ptr += attr_len;
-
+            ptr += jsstr_flush(attr_value, ptr);
             *ptr++ = '"';
             *ptr++ = '>';
             ptr += jsstr_flush(str, ptr);
@@ -249,8 +239,7 @@ static HRESULT do_attribute_tag_format(script_ctx_t *ctx, vdisp_t *jsthis, unsig
         }
     }
 
-    if(attr_value)
-        jsstr_release(attr_value);
+    jsstr_release(attr_value);
     jsstr_release(str);
     return hres;
 }