docs(ol-geom-line-string): add demo for changing coordinates

closes #387

Author: d-koppenhagen

src/demos/LineString.vue

@@ -1,4 +1,8 @@
 <template>
+  <button class="btn-default" @click="addCoordinate" type="button">
+    Add coordinate
+  </button>
+
   <ol-map
     :loadTilesWhileAnimating="true"
     :loadTilesWhileInteracting="true"
@@ -18,26 +22,7 @@
     <ol-vector-layer>
       <ol-source-vector>
         <ol-feature ref="profileFeatureRef">
-          <ol-geom-line-string
-            :coordinates="[
-              [116.544921, 40.451633],
-              [116.545264, 40.451649],
-              [116.545865, 40.451698],
-              [116.546144, 40.451551],
-              [116.546337, 40.451274],
-              [116.546788, 40.451143],
-              [116.547324, 40.451078],
-              [116.547539, 40.450996],
-              [116.547839, 40.450719],
-              [116.54844, 40.450506],
-              [116.548933, 40.450604],
-              [116.549448, 40.450604],
-              [116.550242, 40.450376],
-              [116.550865, 40.450163],
-              [116.551702, 40.449935],
-              [116.552581, 40.449576],
-            ]"
-          ></ol-geom-line-string>
+          <ol-geom-line-string :coordinates="coordinates"></ol-geom-line-string>
           <ol-style>
             <ol-style-stroke
               :color="strokeColor"
@@ -66,6 +51,32 @@ const zoom = ref(17);
 const strokeWidth = ref(10);
 const strokeColor = ref("red");
 const profileFeatureRef = ref(null);
+const coordinates = ref([
+  [116.544921, 40.451633],
+  [116.545264, 40.451649],
+  [116.545865, 40.451698],
+  [116.546144, 40.451551],
+  [116.546337, 40.451274],
+  [116.546788, 40.451143],
+  [116.547324, 40.451078],
+  [116.547539, 40.450996],
+  [116.547839, 40.450719],
+  [116.54844, 40.450506],
+  [116.548933, 40.450604],
+  [116.549448, 40.450604],
+  [116.550242, 40.450376],
+  [116.550865, 40.450163],
+  [116.551702, 40.449935],
+  [116.552581, 40.449576],
+]);
+
+function addCoordinate() {
+  const lastCoordinate = coordinates.value[coordinates.value.length - 1];
+  coordinates.value.push([
+    lastCoordinate[0] + Math.random() * 0.0005,
+    lastCoordinate[1] - Math.random() * 0.0005,
+  ]);
+}
 
 function over(event) {
   console.log(event);