用javascript限制一個文本框只能輸入數字

<input name=mlizhong size=4 value='' maxlength=4
  οnkeypress="return event.keyCode>=48&&event.keyCode<=57"
  οnpaste="var s=clipboardData.getData('text'); if(!//D/.test(s)) value=s.replace(/^0*/,''); return false;" οndragenter="return false"
  style="ime-mode:disabled"  οnkeyup="if(/(^0+)/.test(value))value=value.replace(/^0*/, '')">