Run synchronously when using a name cache or zero workers.

index.js

@@ -12,10 +12,21 @@ function terser(userOptions = {}) {
 
     renderChunk(code, chunk, outputOptions) {
       if (!this.worker) {
-        this.worker = new Worker(require.resolve("./transform.js"), {
-          numWorkers: userOptions.numWorkers
-        });
-        this.numOfBundles = 0;
+        if (userOptions.nameCache || userOptions.numWorkers === 0) {
+          // Transform syncronously
+          this.worker = {
+            transform: function() {
+              const transformer = require("./transform.js");
+              return Promise.resolve(transformer.transform.apply(null, arguments));
+            },
+            end: function() {} // noop
+          };
+        } else {
+          this.worker = new Worker(require.resolve("./transform.js"), {
+            numWorkers: userOptions.numWorkers
+          });
+          this.numOfBundles = 0;
+        }
       }
 
       this.numOfBundles++;
@@ -32,7 +43,9 @@ function terser(userOptions = {}) {
         }
       }
 
-      const serializedOptions = serialize(normalizedOptions);
+      const serializedOptions = (userOptions.nameCache || userOptions.numWorkers === 0) 
+        ? normalizedOptions
+        : serialize(normalizedOptions);
 
       const result = this.worker
         .transform(code, serializedOptions)

transform.js

@@ -1,7 +1,7 @@
 const { minify } = require("terser");
 
 const transform = (code, optionsString) => {
-  const options = eval(`(${optionsString})`);
+  const options = typeof optionsString === 'string' ? eval(`(${optionsString})`) : optionsString;
   const result = minify(code, options);
   if (result.error) {
     throw result.error;