js code to calculate remaining length of text field_javascript skills

JS calculates the number of remaining words in the text field <textarea cols="20" rows="4" onkeyup="displaySpareNumber(this,10)" onchange="displaySpareNumber(this,10)"> <input id="spareNumber" name="spareNumber" value="10" size="1"> Leftover <br> <br><br> Note: <br> displaySpareNumber(this,10) <br> with <br> <input id="spareNumber" name="spareNumber" value="10" size="1"/> The 10 in it is the content length you defined.
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