[Refactor] use call-bound directly; use es-object-atoms

implementation.js

@@ -3,25 +3,25 @@
 // modified from https://github.com/es-shims/es6-shim
 var objectKeys = require('object-keys');
 var hasSymbols = require('has-symbols/shams')();
-var callBound = require('call-bind/callBound');
-var toObject = Object;
+var callBound = require('call-bound');
+var $Object = require('es-object-atoms');
 var $push = callBound('Array.prototype.push');
 var $propIsEnumerable = callBound('Object.prototype.propertyIsEnumerable');
-var originalGetSymbols = hasSymbols ? Object.getOwnPropertySymbols : null;
+var originalGetSymbols = hasSymbols ? $Object.getOwnPropertySymbols : null;
 
 // eslint-disable-next-line no-unused-vars
 module.exports = function assign(target, source1) {
 	if (target == null) { throw new TypeError('target must be an object'); }
-	var to = toObject(target); // step 1
+	var to = $Object(target); // step 1
 	if (arguments.length === 1) {
 		return to; // step 2
 	}
 	for (var s = 1; s < arguments.length; ++s) {
-		var from = toObject(arguments[s]); // step 3.a.i
+		var from = $Object(arguments[s]); // step 3.a.i
 
 		// step 3.a.ii:
 		var keys = objectKeys(from);
-		var getSymbols = hasSymbols && (Object.getOwnPropertySymbols || originalGetSymbols);
+		var getSymbols = hasSymbols && ($Object.getOwnPropertySymbols || originalGetSymbols);
 		if (getSymbols) {
 			var syms = getSymbols(from);
 			for (var j = 0; j < syms.length; ++j) {

package.json

@@ -42,6 +42,7 @@
 	],
 	"dependencies": {
 		"call-bind": "^1.0.8",
+		"call-bound": "^1.0.2",
 		"define-properties": "^1.2.1",
 		"has-symbols": "^1.1.0",
 		"object-keys": "^1.1.1"