diff --git a/implementations/javascript/packages/schema/src/compiler/context.ts b/implementations/javascript/packages/schema/src/compiler/context.ts
index e0e8a48..d2fbf19 100644
--- a/implementations/javascript/packages/schema/src/compiler/context.ts
+++ b/implementations/javascript/packages/schema/src/compiler/context.ts
@@ -103,19 +103,22 @@ export class FunctionContext {
             ... items);
     }
 
-    withCapture(fieldName: string | undefined,
-                sourceExpr: string,
-                ks: (sourceExpr: string) => Item[],
-                withCheck = true): Item
+    withCapture<R>(
+        fieldName: string | undefined, sourceExpr: string, ks: (sourceExpr: string) => R): R
     {
         if (fieldName !== void 0) this.captures.push({ fieldName, sourceExpr });
-        const result = withCheck
-            ? seq(`if (${sourceExpr} !== void 0) `, this.block(() => ks(sourceExpr)))
-            : block(... ks(sourceExpr));
+        const result = ks(sourceExpr);
         if (fieldName !== void 0) this.captures.pop();
         return result;
     }
 
+    convertCapture(
+        fieldName: string | undefined, sourceExpr: string, ks: (sourceExpr: string) => Item[]): Item
+    {
+        return this.withCapture(fieldName, sourceExpr, sourceExpr =>
+            seq(`if (${sourceExpr} !== void 0) `, this.block(() => ks(sourceExpr))));
+    }
+
     buildCapturedCompound(dest: string): Item {
         return seq(`${dest} = `, braces(
             ... variantInitFor(this.variantName),
diff --git a/implementations/javascript/packages/schema/src/compiler/converter.ts b/implementations/javascript/packages/schema/src/compiler/converter.ts
index b4519db..3a8fd4d 100644
--- a/implementations/javascript/packages/schema/src/compiler/converter.ts
+++ b/implementations/javascript/packages/schema/src/compiler/converter.ts
@@ -47,8 +47,7 @@ function converterForAlternative(
             } else if (ctx.variantName !== void 0) {
                 return [ctx.withCapture('value',
                                         simpleValue,
-                                        () => [ctx.buildCapturedCompound(dest)],
-                                        false)];
+                                        () => ctx.buildCapturedCompound(dest))];
             } else {
                 return [`${dest} = ${simpleValue}`];
             }
@@ -102,7 +101,7 @@ function converterForArray(ctx: FunctionContext,
                 ... converterFor(ctx, arrayType, v, vv => [`${r}.push(${vv})`, `continue`]),
                 seq(`${r} = void 0`),
                 seq(`break`)])),
-            ctx.withCapture(M.nameFor(arrayType), r, k)];
+            ctx.convertCapture(M.nameFor(arrayType), r, k)];
     };
     return (checkArray
         ? seq(`if (_.Array.isArray(${src})) `, ctx.block(postCheck))
@@ -122,7 +121,7 @@ function converterFor(
     if (M.isSimplePattern(p)) {
         const dest = ctx.gentemp(typeFor(ctx.mod, p), ` | undefined`);
         return [... converterForSimple(ctx, p, src, dest),
-                ctx.withCapture(maybeName, dest, ks)];
+                ctx.convertCapture(maybeName, dest, ks)];
     } else {
         switch (p.label) {
             case M.$setof: {
@@ -137,7 +136,7 @@ function converterFor(
                                 [`${r}.add(${vv})`, `continue`]),
                             seq(`${r} = void 0`),
                             seq(`break`)])),
-                        ctx.withCapture(maybeName, r, ks)]))];
+                        ctx.convertCapture(maybeName, r, ks)]))];
             }
             case M.$dictof: {
                 const keyPattern = p[0];
@@ -154,7 +153,7 @@ function converterFor(
                                     [`${r}.set(${kk}, ${vv})`, `continue`])),
                             seq(`${r} = void 0`),
                             seq(`break`)])),
-                        ctx.withCapture(maybeName, r, ks)]))];
+                        ctx.convertCapture(maybeName, r, ks)]))];
             }
             default: {
                 const arrayType = M.simpleArray(p);