newMarker 变量的作用域应属于组件，以便您以后能够将其删除。目前，它仅存在于 onClick 方法内。您可以在 此处 阅读有关变量作用域的更多信息。为了解决您的问题，您需要将 newMarker 添加到 data() 函数：

// ...
data() {
  return {
    // ...
    tileLayer: null,
    newMarker: null
  };
},
// ...
onClick(e) {
  this.newMarker = L
    .marker(e.latlng, { draggable: true })
    .addTo(this.map)
    .bindPopup(this.popupContent);

  this.markers.push(this.newMarker);

  this.newMarker.on("popupopen", this.onPopupOpen, this);
},

onPopupOpen(index) {
  $(".marker-delete-button:visible").click(() => {
    this.map.removeLayer(this.newMarker);
  });
}

您的完整代码将类似于：

<template>
  <div id="app" class="container-fluid">
    <div class="row">
      <div class="col-md-9">
        <div id="map" class="map" style="height: 781px;"></div>
      </div>
      <div class="col-md-3">

      </div>
    </div>
    <router-view/>
  </div>
</template>

<script>
export default {
  name: "App",

  data() {
    return {
      map: null,
      markers: [],
      mapSW: [0, 4096],
      mapNE: [4096, 0],
      tileLayer: null,
      newMarker: null
    };
  },

  mounted() {
    this.initMap();
    this.initLayers();
    this.onClick();
    this.onPopupOpen();
  },

  computed: {
    popupContent: function() {
      return "<input type='button' value='Delete' class='marker-delete-button' /> <br> <input type='button' value='Add Event' class='add-event'/>";
    }
  },

  methods: {
    initMap() {
      this.map = L.map("map").setView([0, 0], 1);
      this.tileLayer = L.tileLayer("/static/map/{z}/{x}/{y}.png", {
        maxZoom: 4,
        minZoom: 3,
        continuousWorld: false,
        noWrap: true,
        crs: L.CRS.Simple
      });
      this.tileLayer.addTo(this.map);

      this.map.on("click", this.onClick, this);

      this.map.setMaxBounds(
        L.LatLngBounds(L.latLng(this.mapSW), L.latLng(this.mapNW))
      );
    },

    initLayers() {},

    onClick(e) {
      this.newMarker = L
        .marker(e.latlng, { draggable: true })
        .addTo(this.map)
        .bindPopup(this.popupContent);

      this.markers.push(this.newMarker);

      this.newMarker.on("popupopen", this.onPopupOpen, this);
    },

    onPopupOpen(index) {
      $(".marker-delete-button:visible").click(() => {
        this.map.removeLayer(this.newMarker);
      });
    }
  }
};
</script>

您还可以做的是在删除标记之前验证它是否确实在地图上，使用 hasLayer 方法，如下所示：

if (this.map.hasLayer(this.newMarker)) this.map.removeLayer(this.newMarker);