interactive horizontal limit lines

src/blockchain/common.js

@@ -1,3 +1,23 @@
+
+export function mixin(child, ...parents) {
+    for( const parent of parents ) {
+        for ( const key in parent) {
+            if (parent.hasOwnProperty(key)) {
+                child[key] = parent[key];
+            }
+        }
+    }
+    return child;
+}
+
+
+export function prototype(parent, child) {
+    const result = Object.create(parent);
+    Object.assign(result, child)
+    return result
+}
+
+
 export function encodeIEE754(value) {
     const buffer = new ArrayBuffer(4);
     const view = new DataView(buffer);