JSFiddle - React, Tailwind, and code Playground

HTML

<textarea>char char @char char @char</textarea>

JavaScript

$('textarea').keyup(
    function() {
        var valOfTextarea = $(this).val();
        var splitedVal = valOfTextarea.split(/\s/);
        
        var indexOfAt = $.map(splitedVal, function(o, i){
            return o.indexOf('@') != -1 ? i : null;
        });
        
        console.log(indexOfAt);
        console.log($.map(indexOfAt, function(i){ return splitedVal[i]; }));
    }
);