如何根据textarea中的字符数查找成本

i have a textarea in my form

<textarea id="word_count"></textarea>
Cost <input type="text" value=""/>

I used to find the cost based on number of characters the user enters in the textbox. $50 for each 200 characters. result would be like this

cost = $50 for 200 character 
       $100 for 400 character
       $150 for 600 character

I found the number of characters entering in the textbox.

<script>
  $("#word_count").on('keyup', function() {
    var word_count  =$("#word_count").val().replace(/\s/g, "").length;     
  });
</script>

Prepare a helper json like: var helperJSON ={ 200:'$50', 400: '$100', 600: '$150' }

$("#word_count").on('keyup', function() {
        var word_count=$("#word_count").val().replace(/\s/g, "").length;  
        var cost = helperJSON[word_count];
        if(cost){
          //do something
        }


    });

SO when you capture the characters call the helper variable which will give you the costs.

let characterCount = 650;

let price = Math.floor(characterCount / 200) * 50;
console.log (price);

</div>