function statInputNum( textArea, numItem ) {

 var max = textArea.attr( "maxlength");

 var curLength=0;

 curLength = textArea.val()

   .length;

 numItem.text(max-curLength);

 textArea.on( 'input propertychange', function () {

   var _value = $( this )

     .val()

     .replace( /\n/gi, "" );

    numItem.text( max - _value.length );

 } );

}

text1.on('focus',function(){

statInputNum(text1,len1)

  })

<textarea type="text" style="border:1px solid  #d5d3d3;" class="input" id="operatingIncome" maxlength="50" placeholder="請輸入其他經營收入"></textarea>

 <div class="tooltip"><span id="operatingIncomeNumber">50</span>/50</div>