Javascript Checkbox add value Textarea

I have a code like these:

var fails = 'fail';
var sucs = 'success';

function showSig(i,state){
        if(state){
      document.getElementsByClassName("hasil[]").value=fails;
    }else{
      document.getElementsByClassName("hasil[]").value=sucs;
                                                                                                                }
                                                                                                                
                                                                                                        }

<form>
  <table border='1'>
    <tr>
      <th>TARGET</th>
      <th>RESULT</th>
      <th>NOTES</th>
    </tr>
    <tr>
      <td><input type='checkbox' name='target' onclick='showSig(this.checked);' /></td>
      <td><textarea name='result[]' class='hasil'>fail</textarea></td>       <td><textarea name='notes[]' class='form-control'></textarea></td>
    </tr>
    <tr>
      <td><input type='checkbox' name='target' onclick='showSig(this.checked);' /></td>
      <td><textarea name='result[]' class='hasil'>fail</textarea></td>       <td><textarea name='notes[]' class='form-control'></textarea></td>
    </tr>
    <tr>
      <td><input type='checkbox' name='target' onclick='showSig(this.checked);' /></td>
      <td><textarea name='result[]' class='hasil'>fail</textarea></td>       <td><textarea name='notes[]' class='form-control'></textarea></td>
    </tr>
</form>

I want to create that checkbox, if it's clicked, it will change textarea on that row to success. If I uncheck, it will change back to fail. Can anyone help me?