<div class="input-group" style="margin-top: 10px;">
      <span class="input-group-addon" style="height: 30px;">
          <i class="fa fa-search"></i>
      </span><input id="search_input_unit" type="text" onchange="searchUnit();"
                class="form-control" placeholder="输入内容进行检索"
                style="height: 30px;" />
</div>

function searchUnit (){
    alert(1);
}

searchUnit = function (){
    alert(1);
}

1 Uncaught ReferenceError: searchUnit is not defined
    at HTMLInputElement.onchange

function searchUnit (){
    alert(1);
}
$("#search_input_unit").on("change",searchUnit);