Assuming I have the following:
var array = [ {\"name\":\"Joe\", \"age\":17}, {\"name\":\"Bob\", \"age\":17}, {\"name\":\"Carl\
Simple one-liner with great performance. 6% faster than the ES6 solutions in my tests.
var ages = array.map(function(o){return o.age}).filter(function(v,i,a) { return a.indexOf(v)===i });