使用的是echarts-for-wx插件；
正常写法案例：给tooltip数值加个%

<template>
    <view>
       <uni-ec-canvas 
          class="uni-ec-canvas"
          id="uni-ec-canvas"
          ref="canvas"
          canvas-id="uni-ec-canvas"
          :ec="ec"
       ></uni-ec-canvas>
    </view>
</template>
<script>
// 此处将路径替换为你放置该组件的路径  
import uniEcCanvas from './uni-ec-canvas/ec-canvas.vue'  

export default{
    data(){
        return {
            ec:{
                options:{} //echart 配置项
            }
        }
    },
    components:{
        uniEcCanvas
    },
    mounted(){
		this.initChart()
	},
    methods:{
		initChart(){
			this.ec.option={
				//其他配置项我就不写了，只展示tooltip
				tooltip: {
						trigger: 'axis',
						confine: true, //提示框限制在图形内
						axisPointer: {
							type: 'line',
							axis: 'auto', // 指示器的坐标轴。 
							snap: true, // 坐标轴指示器是否自动吸附到点上
						},
						textStyle: {
							// color: "#fff" //设置文字颜色
						},
						padding: 5, // 提示框浮层内边距，
						formatter: (params)=> {
						        var html = params[0].name + '\n';
						        //资金使用率添加%
						        html +=
						            params[0].marker +
						            params[0].seriesName +
						            '：' +
						            params[0].value +
						            '%'
						        return html;
						}
						// backgroundColor: '#ee6461',
				},
			}
			this.$refs.canvas.init();
		}
	}
}
</script>
// 这里一定要注意 设置该组件宽高 以及display:block来确保canvas初始化的时候是有宽高的
<style>
.uni-ec-canvas{
    width:100%;
    height:100%;
    display:block;
}
</style>

这样的写法formatter自定义是不会生效的；
想要自定义生效的正确写法

this.$refs['canvas'].ec.option={
	tooltip: {
		trigger: 'axis',
		confine: true, //提示框限制在图形内
		axisPointer: {
			type: 'line',
			axis: 'auto', // 指示器的坐标轴。 
			snap: true, // 坐标轴指示器是否自动吸附到点上
		},
		padding: 5, // 提示框浮层内边距，
		formatter: (params)=> {
			var html = params[0].name + '\n';
			//资金使用率添加%
			html +=
				params[0].marker +
				params[0].seriesName +
				'：' +
				params[0].value +
				 '%'
				return html;
			}
	},
}

顺带提一嘴在开发工具上看会有echarts层级太高遮挡显示层问题；这个问题不必理会，真机上显示是正常的

再使用dataZoom组件的时候会报错e.preventDefault is not a function
解决方法
找到echarts组件的vue文件，我的是 uni-ec-canvas.vue

//在触摸事件加上preventDefault: () => {},
stopImmediatePropagation: () => {},
stopPropagation: () => {}

touchStart(e) {
        if (this.ec.stopTouchEvent) {
          e.preventDefault();
          e.stopPropagation();
          return;
        }
        this.$emit("touchstart", e);
        if (this.$curChart && e.touches.length > 0) {
          var touch = e.touches[0];
          var handler = this.$curChart.getZr().handler;
          if (handler) {
            handler.dispatch("mousedown", {
              zrX: touch.x,
              zrY: touch.y,
							//需要添加的方法即可解决dataZoom报错
							preventDefault: () => {},
							stopImmediatePropagation: () => {},
							stopPropagation: () => {}
            });
            handler.dispatch("mousemove", {
              zrX: touch.x,
              zrY: touch.y,
							//需要添加的方法即可解决dataZoom报错
							preventDefault: () => {},
							stopImmediatePropagation: () => {},
							stopPropagation: () => {}
            });
            handler.processGesture(wrapTouch(e), "start");
          }
        }
},

touchMove(e) {
        if (this.ec.stopTouchEvent) {
          e.preventDefault();
          e.stopPropagation();
          return;
        }
        this.$emit("touchmove", e);
        if (this.$curChart && e.touches.length > 0) {
          var touch = e.touches[0];
          var handler = this.$curChart.getZr().handler;
          if (handler) {
            handler.dispatch("mousemove", {
              zrX: touch.x,
              zrY: touch.y,
							//需要添加的方法即可解决dataZoom报错
							preventDefault: () => {},
							stopImmediatePropagation: () => {},
							stopPropagation: () => {}
            });
            handler.processGesture(wrapTouch(e), "change");
          }
        }
},

touchEnd(e) {
        if (this.ec.stopTouchEvent) {
          e.preventDefault();
          e.stopPropagation();
          return;
        }
        this.$emit("touchend", e);
        if (this.$curChart) {
          const touch = e.changedTouches ? e.changedTouches[0] : {};
          var handler = this.$curChart.getZr().handler;
          if (handler) {
            handler.dispatch("mouseup", {
              zrX: touch.x,
              zrY: touch.y,
							//需要添加的方法即可解决dataZoom报错
							preventDefault: () => {},
							stopImmediatePropagation: () => {},
							stopPropagation: () => {}
            });
            handler.dispatch("click", {
              zrX: touch.x,
              zrY: touch.y,
							//需要添加的方法即可解决dataZoom报错
							preventDefault: () => {},
							stopImmediatePropagation: () => {},
							stopPropagation: () => {}
            });
            handler.processGesture(wrapTouch(e), "end");
          }
        }
},