addItem.js

/**
 * addItem
 * adding item into existing array by matching id
 */
function addItem(item, currentArrayOfItem) {    
    let exist = currentArrayOfItem.find(_item => _item.id === item.id);
    if (exist) {        
        let index = currentArrayOfItem.indexOf(exist);
        currentArrayOfItem.splice(index, 1, item); // reason: reactivity
    } else {        
        currentArrayOfItem.unshift(item);
    }
}