Selected items is not setting the value by default.
here is my code.
Hello Yui Chan,
Thank you for contacting us.
I am sending you a link where I have made an example on jsfiddle based on your requirement. There you can see how to set items to be selected with initialSelectedItems option on combo initialization. In addition, you can initialize the combo with default selected items with the value, index and select methods.
Let me know if you have any further questions.