Lodash intersperse

intersperse.js

function intersperse(a, f) {
  var pairs = _.zip(
    _.tail(a),
    _.slice(a, 0, -1)
  );
  
  var inner = _.map(pairs, _.isFunction(f) ? _.spread(f) : _.constant(f));

  var result = _.chain(a)
    .zip(inner)
    .flatten()
    .slice(0, -1)
    .value();
    
  return result;
}