The principle and example of jQuery determining whether a check box is checked_jquery

Today I want to implement a function: assign a value to the input form when the check box is checked, and clear the form value when the check box is cancelled.

The effect is as shown:

Implementation source code: cyfID is the id of the check box

Copy code The code is as follows:

$("#cyfID").click(function(){
var ischeck=$(this).attr("checked");
if(ischeck==undefined){
//Clear the input box
alert("");
}else{
//Assign a value to the input box
alert("qq" );
}
});

The implementation principle is: $(this).attr("checked") is checked when the check box is checked, and it is checked when it is not checked. undefined.