live-test & show valid starting identifier characters in js.

ShowValidStartingIdentifierChars.js

+function ShowValidStartingIdentifierChars(){
var validStarters={}
,max=130000
,group=5000
for(var i=0;i<max;i++){
 try{
  var s=String.fromCodePoint(i)
  eval(`let ${s}=1`)
  validStarters[s]=1
 }
 catch(e){ }
}

var st=document.createElement("style")

st.innerHTML=`
span {
	display: inline-block;
	outline: solid #000 1px;
	padding: .25em;
	font-size: 2em;
	background-color:#fff;
	transition:transform ease-in .0625s;
}

span:hover{
	transform:scale(2);
}
`
document.body.appendChild(st)

var d
Object.keys(validStarters).forEach((x,i)=>{
 if( !(i%group) ){
  if(d) document.body.appendChild(d)
  d=document.createElement("details")
  d.innerHTML=`<summary>${i} - ${i+group}`
 }
 var s=document.createElement("span")
 s.innerHTML=x
 s.setAttribute("title",x.codePointAt(0))
 d.appendChild(s)
})

}()