In accordance with an embodiment, described herein is a system and method for supporting JavaScript as an expression language in an executable process defined by a process execution language. An extension namespace to the process execution language can be used to define additional attributes for supporting JavaScript as an expression language. Used as an expression language, JavaScript can be used to access contents of XML variables in the executable process without the need to walk through complicated XML structures of the XML variables. A JavaScript expression can be used anywhere an XPath expression can be used, and can additionally be used to access a plurality of functions and variables that cannot be accessed using an XPath expression. A process execution engine can be provided on one or more application servers in a SOA middleware environment to host the executable process, wherein the process execution engine can include a JavaScript engine to interpret JavaScript expressions in the executable process.