Function optimizeCb

underscore.js:745–762

(func, context, argCount)

  // of the passed-in callback, to be repeatedly applied in other Underscore
  // functions.
  function optimizeCb(func, context, argCount) {
    if (context === void 0) return func;
    switch (argCount == null ? 3 : argCount) {
      case 1: return function(value) {
        return func.call(context, value);
      };
      // The 2-argument case is omitted because we’re not using it.
      case 3: return function(value, index, collection) {
        return func.call(context, value, index, collection);
      };
      case 4: return function(accumulator, value, index, collection) {
        return func.call(context, accumulator, value, index, collection);
      };
    }
    return function() {
      return func.apply(context, arguments);
    };
  }

  // An internal function to generate callbacks that can be applied to each
  // element in a collection, returning the desired result — either `_.identity`,