Because I want to judge the compatibility of browser monitoring, so write this below
Element["on "plus type]=handler;
My understanding is that this formula obtains the following sentence pattern
But what I really want is (I think this is right)
Question: Why did he use  instead of. () to wrap the contents inside? ? Which piece of knowledge is this? ?
Expression.identifier // An expression specifies an object and an identifier specifies the name of the attribute that needs to be accessed Expression[expression] // This method is applicable to objects and arrays. The expression in  specifies the name of the attribute to be accessed or represents the index of the array element to be accessed.
.identifierThe writing of is only applicable to the identifier that the attribute name to be accessed is legal, andYou need to know the name of the attribute you want to access..
When the attribute name is a calculated value instead of a fixed value, square brackets must be used.
Element["on "plus type]=handler; //type here is a string, so this attribute is formed by concatenation of strings and is calculated. Therefore, access to this attribute can only be written in square brackets.
When the event type (such as click event) is determined, you can register directly as follows:
element["onclick"]=handler;(the subject’s code is short of quotation marks) or