Error if duplicate keys are present

tbranyen · Jul 23, 2017 · a003f3a · a003f3a
1 parent 6379f45
commit a003f3a
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Showing 2 changed files with 31 additions and 0 deletions.
diff --git a/packages/diffhtml/lib/tree/sync.js b/packages/diffhtml/lib/tree/sync.js
@@ -44,6 +44,12 @@ export default function syncTree(oldTree, newTree, patches, parentTree, specialC
         const vTree = nodes[i];
 
         if (vTree.key) {
+          if (process.env.NODE_ENV !== 'production') {
+            if (map.has(vTree.key)) {
+              throw new Error(`Key: ${vTree.key} cannot be duplicated`);
+            }
+          }
+
           map.set(vTree.key, vTree);
         }
       }

diff --git a/packages/diffhtml/test/tree.js b/packages/diffhtml/test/tree.js
@@ -750,6 +750,31 @@ describe('Tree', function() {
     });
 
     describe('Elements (keyed)', () => {
+      it('will error if duplicate keys are provided in development', () => {
+        const referenceNode = createTree('div', { key: '0' });
+        const duplicateNode = createTree('div', { key: '0' });
+        const oldTree = createTree('div', null, [referenceNode]);
+        const newTree = createTree('div', null, [
+          referenceNode,
+          duplicateNode,
+        ]);
+
+        throws(() => syncTree(oldTree, newTree));
+      });
+
+      it('will not error if duplicate keys are provided in production', () => {
+        const referenceNode = createTree('div', { key: '0' });
+        const duplicateNode = createTree('div', { key: '0' });
+        const oldTree = createTree('div', null, [referenceNode]);
+        const newTree = createTree('div', null, [
+          referenceNode,
+          duplicateNode,
+        ]);
+
+        process.env.NODE_ENV = 'production';
+        doesNotThrow(() => syncTree(oldTree, newTree));
+      });
+
       describe('insertBefore', () => {
         it('will prepend an element', () => {
           const referenceNode = createTree('div', { key: '0' });