var str="javascript coffeescript vbscript javacode"
var re2=/(?=java)\b\w+script\b/g
console.log(str.match(re2))
var str="dog,cat,pig,cow"
var re2=/\b\w+\b(?=,cat|,pig)/g
console.log(str.match(re2))
Ответ:
[ 'javascript' ]
[ 'dog', 'cat' ]
JavaScript test | #JavaScript