Bump to v4.0.0.

bindKey.js

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+import createWrapper from './internal/createWrapper';
+import replaceHolders from './internal/replaceHolders';
+import rest from './rest';
+
+/** Used to compose bitmasks for wrapper metadata. */
+var BIND_FLAG = 1,
+    BIND_KEY_FLAG = 2,
+    PARTIAL_FLAG = 32;
+
+/**
+ * Creates a function that invokes the method at `object[key]` and prepends
+ * any additional `_.bindKey` arguments to those provided to the bound function.
+ *
+ * This method differs from `_.bind` by allowing bound functions to reference
+ * methods that may be redefined or don't yet exist.
+ * See [Peter Michaux's article](http://peter.michaux.ca/articles/lazy-function-definition-pattern)
+ * for more details.
+ *
+ * The `_.bindKey.placeholder` value, which defaults to `_` in monolithic
+ * builds, may be used as a placeholder for partially applied arguments.
+ *
+ * @static
+ * @memberOf _
+ * @category Function
+ * @param {Object} object The object to invoke the method on.
+ * @param {string} key The key of the method.
+ * @param {...*} [partials] The arguments to be partially applied.
+ * @returns {Function} Returns the new bound function.
+ * @example
+ *
+ * var object = {
+ *   'user': 'fred',
+ *   'greet': function(greeting, punctuation) {
+ *     return greeting + ' ' + this.user + punctuation;
+ *   }
+ * };
+ *
+ * var bound = _.bindKey(object, 'greet', 'hi');
+ * bound('!');
+ * // => 'hi fred!'
+ *
+ * object.greet = function(greeting, punctuation) {
+ *   return greeting + 'ya ' + this.user + punctuation;
+ * };
+ *
+ * bound('!');
+ * // => 'hiya fred!'
+ *
+ * // using placeholders
+ * var bound = _.bindKey(object, 'greet', _, '!');
+ * bound('hi');
+ * // => 'hiya fred!'
+ */
+var bindKey = rest(function(object, key, partials) {
+  var bitmask = BIND_FLAG | BIND_KEY_FLAG;
+  if (partials.length) {
+    var holders = replaceHolders(partials, bindKey.placeholder);
+    bitmask |= PARTIAL_FLAG;
+  }
+  return createWrapper(key, bitmask, object, partials, holders);
+});
+
+export default bindKey;