如何将javascript变量值从选定的文本框设置为另一个文本框

I'm using onclick javascript alert to show my selected value from textbox. Now I want to set these value to another textbox. I am new to javascript help me if u can. I want these two values into two textboxes but don't how it is possible.Here is my code.

onClick="javascript:alert('Date select from '+this.form.date3.value+' to '+this.form.date4.value);"

You can set value like this..

document.getElementid('Textbox1').value=this.form.date3.value;
document.getElementid('Textbox2').value=this.form.date4.value;