JSFiddle - React, Tailwind, and code Playground

HTML

t must have a['test']
s must NOT have a['test']

JavaScript

var s = {
    a: [],
    
    add: function(s) {
        this.a.push(s);
    }
}
    
    var t = $.extend({}, s);


t.add('test');

console.log(t);
console.log(s);