JSFiddle - React, Tailwind, and code Playground

HTML

<form textarea name="a">Text "A" : <input name="a" /></textarea> </form>
<br />
<form name="b">Text "B" : <input name="a" /></form>
<hr>
<button>check</button>

JavaScript

var doc=document;
doc.body.onclick=function(){
    var arr=doc.b.a.value.split(" ");
    for(var i=0; i<arr.length; i++) {
        if(doc.a.a.value.indexOf(arr[i])+1==0){
          alert(arr[i]);
        }
    }   
}