There is a piece of code that I am confused about
var clickEventType=((document.ontouchstart!==null)?'click':'touchstart');If it says document.ontouchstart!==null, it means that touchstart exists, and it should look like this:
var clickEventType=((document.ontouchstart!==null)?'touchstart':'click')Why is it written the way above?
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If written as
You will understand,
ontoucstartis an attribute of thedoucmentobject, butontouchstartpoints to a reference to the function, that is,ontouchstartpoints to an object. When it is not pointed to,ontouchstartneeds an initial value. This initial value isnull. If thetouchstartevent is supported, then the initial value of ontouchstart is set tonull, so it is written like thisThis shows that the current browser supports ontouchstart, because if it does not support it, the value of
document.ontouchstartisundefined, and if
document.ontouchstartis not bound to the event, it is equal to null, so you You can use it like thisdocument.ontouchstart = function(){};The initial value is Null. If it is not equal to null, it can be said that it is not supported