主题：js怎么实现工资 +奖金 +其他 =年收入合计 并显示在年收入合计数据框里呢？

<form class="layui-form model-form no-padding layui-form-pane" style="color: #B896E8" lay-filter="lrform" id="lrform">
    <div class="layui-form-item model-form-footer text-center">
        <button class="layui-btn" lay-filter="lrform-submit" lay-submit>确认</button>
        <button class="layui-btn layui-btn-primary" type="button" ew-event="closeDialog">取消</button>
    </div>           
    <fieldset class="layui-elem-field layui-field-title" style="margin-top: 20px;">
        <legend>收入情况</legend>
    </fieldset>
 <div class="layui-row layui-col-space8">
  
 <div class="layui-col-md4">
  <div class="layui-form-item">
   <label class="layui-form-label">年收入合计</label>
   <div class="layui-input-block">
    <input type="number" name="年收入合计" id="nianshouruheji_20"  lay-verify="" value="" placeholder="" autocomplete="off" class="layui-input ">
   </div>
  </div>
 </div>
 <div class="layui-col-md4">
  <div class="layui-form-item">
   <label class="layui-form-label">工资</label>
   <div class="layui-input-block">
    <input type="number" name="工资" id="gongzi_21"  lay-verify="" value="" placeholder="" autocomplete="off" class="layui-input " onc han ge="jisuan()">
   </div>
  </div>
 </div>
 <div class="layui-col-md4">
  <div class="layui-form-item">
   <label class="layui-form-label">奖金</label>
   <div class="layui-input-block">
    <input type="number" name="奖金" id="jiangjin_22"  lay-verify="" value="" placeholder="" autocomplete="off" class="layui-input " onc han ge="jisuan()">
   </div>
  </div>
 </div>
 <div class="layui-col-md4">
  <div class="layui-form-item">
   <label class="layui-form-label">其他</label>
   <div class="layui-input-block">
    <input type="number" name="其他" id="qita_23"  lay-verify="" value="" placeholder="" autocomplete="off" class="layui-input " onc han ge="jisuan()">
   </div>
  </div>
 </div>

 </div>

function jisuan(){
document.getElementById('nianshouruheji_20').value =document.getElementById('gongzi_21').value + document.getElementById('jiangjin_22').value + document.getElementById('qita_23').value；
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