Euro currency formatting in Svelte 3 using various options

_ Euro.svelte

<script>
  import { toEur, setFormat } from './use_format.js';
  
  let num = -5;
  setFormat('currency', {style: 'currency', zero:false});

  function handleClick() {
	num <= 0 ? num +=1 : num-=4;
  }

</script>

<style>
  p {
	font-style: italic; 
	font-family: 'Courier New', Courier, monospace
  }
  span {
	font-weight: bold;
	font-style: initial;
  }	
</style>

<h3>Reactive euro formatting</h3>

<p>decimal_0: <span use:toEur={num}></span> setFormat default options(style: 'decimal', zero:true)</p>
<p>currency: <span use:toEur={num, 'currency'}></span> setFormat options(style: 'currency', zero:false)</p>

<button on:click={handleClick}>
	Click {num}
</button>

use_format.js

const formats = {};           // temp formasts store

const default_options = {
  style: "decimal",           // "currency" || "decimal",
  currency: "EUR",
  useGrouping: true,
  minimumFractionDigits: 2,
  zero: true                  // show 0 || ''; Not a NumberFormat option! 
};

export function setFormat(fId, options) {
  // merge options and init formatter
  const format_options = { ...default_options, ...options };
  formats[fId] = {
    options: format_options,
    formatter: new Intl.NumberFormat("nl-NL", format_options),
  };
  console.log('setFormat', fId, format_options)
};
setFormat('decimal_0', {});

// Example: setFormat('currency', {style: 'currency', zero:false});
function formatNode(node, num, formatObj) {
  // format Node (num) using the formatObj initialized formatter (options)
  let number = ('' + num).trim();
  // handle the zero option
  if (formatObj.options.zero === false && (number === '0' || number === '')) node.innerText = '';
  else {
    node.textContent = formatObj.formatter.format(((number || 0) / 100).toFixed(2));
    Object.assign(node.style, {
      color: number.startsWith('-') ? 'red' : 'inherit'
    });  
  }
}

// <p>default: <span use:toEur={num}></span></p>
// <p>currency: <span use:toEur={num, 'currency'}></span></p>
export function toEur(node, num, fId = 'decimal_0') {
  // the node has been mounted in the DOM
  formatNode(node, num, formats[fId])
  return {
    update(num) {  // make it reactive
      // console.log('use_format updated', num, fId);
      formatNode(node, num, formats[fId]);
      // the value of `bar` has changed
    },
    destroy() {
      // the node has been removed from the DOM
    }
  };
}