JS limits the type and size of uploaded files

var maxsize = 6*1024*1024;//6m
var errmsg = "Uploaded attachment file cannot exceed 6m!!! ";
var tipmsg = "Your browser does not support the calculation of upload file size, make sure to upload files not more than 6M, we recommend using IE, FireFox, Chrome browser." ";
var browsercfg = {};
var ua = window.navigator.userAgent;
if (Ua.indexof ("MSIE") >=1) {
Browsercfg.ie = true;
}else if (Ua.indexof ("Firefox") >=1) {
Browsercfg.firefox = true;
}else if (Ua.indexof ("Chrome") >=1) {
Browsercfg.chrome = true;
}

Function Checkfile () {
try{
var obj_file = document.getElementById ("Instructionname");
if (obj_file.value== ") {
Alert (" Please select Upload file ");
return;
}
if (!/\. doc|xls|pdf|xlsx|pptx|docx|ppt) $/.test (obj_file) {
Alert ("Upload file can only be doc|xls|pdf|xlsx|pptx|docx|ppt as suffix file");
$ ("#instructionName"). Val (');
return;
}
var filesize = 0;
if (Browsercfg.firefox | | browsercfg.chrome) {
FileSize = obj_file.files[0].size;
}else if (browsercfg.ie) {
var obj_img = document.getElementById (' tempimg ');
Obj_img.dynsrc=obj_file.value;
FileSize = obj_img.filesize;
}else{
Alert (tipmsg);
$ ("#instructionName"). Val (');
return;
}
if (filesize==-1) {
alert (tipmsg);
return;
}else if (filesize>maxsize) {
alert (errmsg);
return;
}else{
document.getElementById ("Bigsmall"). Value=filesize;
return;
}
}catch (e) {
alert (e);
}
}

<input id= "Instructionname" type= "file" Name= "Instructionname" value= "" onchange= "Checkfile ()" style= "width:80"/ >

<input type= "hidden" id= "Bigsmall" name= "Bigsmall" value= ""/>

JS limits the type and size of uploaded files