Ext中new 和create的區別
1、在Ext JS 4版本之前，一直使用new關鍵字建立物件，其語法如下：
new classname([config])
其中calssname是指類名；config是可選引數，為類的配置物件（config options），型別為JSON物件
2、Ext.create方法是新增的建立物件的方法，其語法如下：
Ext.create(classname,[config])
其中classname可以是類的全名、別名或備用名；config是可選引數，為類的配置物件（config options），型別為物件。
Ext.create和new
Ext.create provides a higher level control for instantiation throughout. It's best practice from Ext JS 4 onwards to use it over the 'new' keyword, since it's tightly coupled
with Ext.Loader which makes dependency resolution much easier. During development the target class will be automatically loaded synchronously the first time it's used, which frees you from having to remember "Ext.require-ing" it before-hand.
Besides, just like Ext.require, Ext.create accepts either a class name or an alias, which makes it extremely convenient to instantiate almost everything in Ext JS 4 library by its xtype / type without having to figure out its full class name up front, for example:
Ext.create('widget.combobox'); // instead of Ext.create('Ext.form.field.ComboBox') Ext.create('proxy.jsonp'); // instead of Ext.create('Ext.data.proxy.JsonP')
Debugging is much more easier. If you try to instantiate a nonexistent class with the 'new' keyword, it's painful to figure out quickly what's going on with "TypeError: undefined is not a function", for example, try:
new Ext.data.proxy.JsonD
instead
Ext.create('Ext.data.proxy.JsonD')
gives you:
[Ext.create] Cannot create an instance of unrecognized class name / alias: Ext.data.proxy.JsonD
We've heavily optimized it internally for the best performance possible, and extreme benchmarks prove no considerable hit on performance over thousands of objects.
Another robust feature with Ext.create that can't be simply achieve with the 'new' keyword is it enables instantiation with variable arguments. For example:
Ext.create.apply(null, ['My.ClassName', arg1, arg2, arg3, ...]);
Which is not possible with:
new My.ClassName({list of arguments must be known here});