JSFiddle - React, Tailwind, and code Playground

HTML

<script src="//cdnjs.cloudflare.com/ajax/libs/knockout.mapping/2.4.1/knockout.mapping.js"></script>
<button data-bind="click: function(){ alert(diff());console.log(diff()) }">Array itself</button>
<button data-bind="click: check">Inside function</button>

JavaScript

var vm = function(){
    var self = this;
    self.orig = ko.observableArray([{
        somevalue: ko.observable("testst")
    }]);
    
    self.diff = ko.observableArray([]);
    
    self.init = function() {
        console.log(ko.toJS(self.orig));
        self.diff(ko.toJS(self.orig));
    }
    
    setTimeout(self.init,2000);
    
    return {
        check: function() { alert(self.diff());console.log(self.diff());},
        diff: self.diff
    }
}

ko.applyBindings(new vm())