EmEditor utilize the ‘Windows Script Host’, which in turn utilize JScript 5.7 feature set.
Even as WSH says it’s 5.8
jsV = ScriptEngineMajorVersion() +"."+ ScriptEngineMinorVersion(); alert(jsV); // 5.8
Note Starting with JScript 5.8, by default,
the JScript scripting engine supports the language feature set as it existed in version 5.7.
This is to maintain compatibility with the earlier versions of the engine.
JScript 5.8 introduced the following features: JSON object, JSON.parse method,
JSON.stringify method, toJSON method, defineProperty method, getOwnPropertyDescriptor method.
And further see: http://stackoverflow.com/questions/19445189/cscript-jscript-json
and perhaps: https://en.wikipedia.org/wiki/Windows_Script_Host