JSFiddle - React, Tailwind, and code Playground

HTML

<div>
    <input type="text" value="0" id="test-input"/>        
    <input type="button" value="Up!" id="test-button" />
</div>

CSS

div {
    width: 300px;
    margin: 50px auto 0;
}

#test-input {
    padding: 2px 4px;
}

#test-button {
    padding: 3px 8px;
}

JavaScript

var scopeTest = {
    
    parseValue : function( element ) {
        var value = parseInt( element.val(), 10 );
        return value;
    },
    
    
    incrementValue : function( element, button ) {
        button.on('mousedown', function (e) {
            var inputVal = scopeTest.parseValue( element );        
            element.val( inputVal + 10 );    
            e.preventDefault(); 
        });               
    },
        
    
    init : function () { 
        var element = $('#test-input'),
            button = $('#test-button');
        
        this.incrementValue( element, button );
    }
        
};

scopeTest.init();