At Khan Academy we use a helper called intersperse
for this:
/* intersperse: Return an array with the separator interspersed between
* each element of the input array.
*
* > _([1,2,3]).intersperse(0)
* [1,0,2,0,3]
*/
function intersperse(arr, sep) {
if (arr.length === 0) {
return [];
}
return arr.slice(1).reduce(function(xs, x, i) {
return xs.concat([sep, x]);
}, [arr[0]]);
}
which allows you to write code like:
var tags = item.tags.map(function(tag, i) {
return <Tag key={i} tag={item.tags[i]} />;
};
tags = intersperse(tags, ", ");