app/javascript/vue/tasks/loans/new/store/mutations/addLoanItem.js
export default (state, loan_item) => {
const position = state.loan_items.findIndex(item => item.id === loan_item.id)
if (position < 0) {
state.loan_items.push(loan_item)
} else {
state.loan_items[position] = loan_item
}
}