Javascript prohibits backspace key (Backspace) example code_javascript skills

Copy code The code is as follows:

function banBackSpace(e) {
var ev = e || window.event; //Get the event object
var obj = ev.target || ev.srcElement;//Get the event source
var t = obj.type || obj.getAttribute('type');/ /Get the event source type
//Get the event type used as the judgment condition var vReadOnly = obj.readOnly;
var vDisabled = obj.disabled;
                                                                                                              vReadOnly = (vReadOnly == undefined) ? false : vReadOnly;
vDisabled = (vDisabled == undefined) ? true : vDisabled;
//When the Backspace key is pressed, the event source type is password or single or multi-line text " text" || t == "textarea") && (vReadOnly == true || vDisabled == true);
                           //When the Backspace key is pressed, the event source type is not a password or a single line or multi-line text, then The backspace key is invalid
var flag2 = ev.keyCode == 8 && t != "password" && t != "text" && t != "textarea";
                                 (flag2 || flag1) return false

                                                                                                                                                       
document.onkeydown = banBackSpace;