js实现圆盘记速表

var chart = AmCharts.makeChart("chartdiv", {        "type": "gauge",        "theme": "none",        "axes": [{          "axisThickness": 1,          "axisAlpha": 0.2,          "tickAlpha": 0.2,          "valueInterval": 20,          "bands": [{            "color": "#84b761",            "endValue": 90,            "startValue": 0          }, {            "color": "#fdd400",            "endValue": 130,            "startValue": 90          }, {            "color": "#cc4748",            "endValue": 220,            "innerRadius": "95%",            "startValue": 130          }],          "bottomText": "0 km/h",          "bottomTextYOffset": -20,          "endValue": 320        }],        "arrows": [{}]      });      window.onload=function(){        chart.arrows[0].setValue(80);        chart.axes[0].setBottomText(80  " km/h");      }      document.getElementById("btnSure").onclick=function(){        if(document.getElementById("txtNum").value>320){          alert("超出最大值");          return;        }        if(document.getElementById("txtNum").value<0){          alert("不能低于0");          return;        }        chart.arrows[0].setValue(document.getElementById("txtNum").value);        chart.axes[0].setBottomText(document.getElementById("txtNum").value  " km/h");      }

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