The memory isolation mechanism plays an essential role to provide security enforcement in JavaScript programs. Existing secure interaction libraries such as Google Caja, SES, and VM2 rely on built-in memory isolation mechanisms provided by Node.js and browsers, yet most of the other engines such as JerryScript and Duktape, which are implementations for IoT devices, do not support such isolation mechanisms.In this paper, we report about the design and implementation of SecureJS, a portable JavaScript-to-JavaScript compiler that enforces memory isolation. As it only uses standard features, the compiled code it generates can be used by any JavaScript engine. We validated empirically the semantics preservation and memory isolation of SecureJS compiled programs by using 10,490 test programs of ECMAScript Test262 test suite. We also developed a novel experiment to evaluate memory isolation property of compiled code by instrumented JavaScript engines.