Testing different possible implementations for lodash to add an intersperse method in https://github.com/lodash/lodash/issues/2339

intersperse.js

```
_.intersperse(["a", "b", "c"], "+");
// ["a", "+", "b", "+", "c"]

intersperse = function intersperse(arr, sep) {
    var i = arr.length,
        separr;
    
    if (!i) return [];
    if (i < 2) return arr.slice();
    
    i  = i * 2 - 1;
    separr = new Array(i);
    
    while (i--) {
        separr[i] = i % 2 === 0 ? arr[Math.floor(i / 2)] : sep;
    }
    
    return sep;
};
```

function intersperse(arr, obj) {
    if (!arr.length) return [];
    if (arr.length === 1) return arr.slice(0);

    var items = [arr[0]];
    for (var i = 1, len = arr.length; i < len; ++i) {
        items.push(obj, arr[i]);
    }

    return items;
}

/**
 * Creates an array in which the contents of the given array are interspersed
 * with... something. If that something is a function, it will be called on each
 * insertion.
 */
function intersperse(array, something) {
  if (array.length < 2) { return array }
  var result = [], i = 0, l = array.length
  if (typeof something == 'function') {
    for (; i < l; i ++) {
      if (i !== 0) { result.push(something()) }
      result.push(array[i])
    }
  }
  else {
    for (; i < l; i ++) {
      if (i !== 0) { result.push(something) }
      result.push(array[i])
    }
  }
  return result
}