The way I'm doing it is to save that properties into an array and after that to join them.
Original array of objects:
const objArray = [ { prop: "a", etc: 1}, { prop: "b", etc: 2}, { prop: "c", etc: 3} ];
First step, save the values of property prop into an array:
const firstStep = objArray.map(a => a.prop);
Second step, concatenate them into a string:
const secondStep = firstStep.join(' + ');
This works fine but I'm thinking if there is a better/shorter method to do this. Any ideas?