lodash/internal/bindCallback.js

define(['../utility/identity'], function(identity) {

  /**
   * A specialized version of `baseCallback` which only supports `this` binding
   * and specifying the number of arguments to provide to `func`.
   *
   * @private
   * @param {Function} func The function to bind.
   * @param {*} thisArg The `this` binding of `func`.
   * @param {number} [argCount] The number of arguments to provide to `func`.
   * @returns {Function} Returns the callback.
   */
  function bindCallback(func, thisArg, argCount) {
    if (typeof func != 'function') {
      return identity;
    }
    if (typeof thisArg == 'undefined') {
      return func;
    }
    switch (argCount) {
      case 1: return function(value) {
        return func.call(thisArg, value);
      };
      case 3: return function(value, index, collection) {
        return func.call(thisArg, value, index, collection);
      };
      case 4: return function(accumulator, value, index, collection) {
        return func.call(thisArg, accumulator, value, index, collection);
      };
      case 5: return function(value, other, key, object, source) {
        return func.call(thisArg, value, other, key, object, source);
      };
    }
    return function() {
      return func.apply(thisArg, arguments);
    };
  }

  return bindCallback;
});