Add JSON support to localStorageSync component

https://gitlab.com/gitlab-org/gitlab/-/merge_requests/42938

app/assets/javascripts/vue_shared/components/local_storage_sync.vue

 <script>
+import { isEqual } from 'lodash';
+
 export default {
   props: {
     storageKey: {
@@ -6,31 +8,58 @@ export default {
       required: true,
     },
     value: {
-      type: String,
+      type: [String, Number, Boolean, Array, Object],
       required: false,
       default: '',
     },
+    asJson: {
+      type: Boolean,
+      required: false,
+      default: false,
+    },
   },
   watch: {
     value(newVal) {
-      this.saveValue(newVal);
+      this.saveValue(this.serialize(newVal));
     },
   },
   mounted() {
     // On mount, trigger update if we actually have a localStorageValue
-    const value = this.getValue();
+    const { exists, value } = this.getStorageValue();
 
-    if (value && this.value !== value) {
+    if (exists && !isEqual(value, this.value)) {
       this.$emit('input', value);
     }
   },
   methods: {
-    getValue() {
-      return localStorage.getItem(this.storageKey);
+    getStorageValue() {
+      const value = localStorage.getItem(this.storageKey);
+
+      if (value === null) {
+        return { exists: false };
+      }
+
+      try {
+        return { exists: true, value: this.deserialize(value) };
+      } catch {
+        // eslint-disable-next-line no-console
+        console.warn(
+          `[gitlab] Failed to deserialize value from localStorage (key=${this.storageKey})`,
+          value,
+        );
+        // default to "don't use localStorage value"
+        return { exists: false };
+      }
     },
     saveValue(val) {
       localStorage.setItem(this.storageKey, val);
     },
+    serialize(val) {
+      return this.asJson ? JSON.stringify(val) : val;
+    },
+    deserialize(val) {
+      return this.asJson ? JSON.parse(val) : val;
+    },
   },
   render() {
     return this.$slots.default;

spec/frontend/helpers/local_storage_helper.js

@@ -35,7 +35,7 @@ export const createLocalStorageSpy = () => {
     clear: jest.fn(() => {
       storage = {};
     }),
-    getItem: jest.fn(key => storage[key]),
+    getItem: jest.fn(key => (key in storage ? storage[key] : null)),
     setItem: jest.fn((key, value) => {
       storage[key] = value;
     }),

spec/frontend/helpers/local_storage_helper_spec.js

@@ -18,11 +18,11 @@ describe('localStorage helper', () => {
 
     localStorage.removeItem('test', 'testing');
 
-    expect(localStorage.getItem('test')).toBeUndefined();
+    expect(localStorage.getItem('test')).toBe(null);
     expect(localStorage.getItem('test2')).toBe('testing');
 
     localStorage.clear();
 
-    expect(localStorage.getItem('test2')).toBeUndefined();
+    expect(localStorage.getItem('test2')).toBe(null);
   });
 });

spec/frontend/vue_shared/components/local_storage_sync_spec.js

@@ -12,7 +12,9 @@ describe('Local Storage Sync', () => {
   };
 
   afterEach(() => {
-    wrapper.destroy();
+    if (wrapper) {
+      wrapper.destroy();
+    }
     wrapper = null;
     localStorage.clear();
   });
@@ -45,23 +47,23 @@ describe('Local Storage Sync', () => {
       expect(wrapper.emitted('input')).toBeFalsy();
     });
 
-    it('saves updated value to localStorage', () => {
-      createComponent({
-        props: {
-          storageKey,
-          value: 'ascending',
-        },
-      });
-
-      const newValue = 'descending';
-      wrapper.setProps({
-        value: newValue,
-      });
-
-      return wrapper.vm.$nextTick().then(() => {
-        expect(localStorage.getItem(storageKey)).toBe(newValue);
-      });
-    });
+    it.each('foo', 3, true, ['foo', 'bar'], { foo: 'bar' })(
+      'saves updated value to localStorage',
+      newValue => {
+        createComponent({
+          props: {
+            storageKey,
+            value: 'initial',
+          },
+        });
+
+        wrapper.setProps({ value: newValue });
+
+        return wrapper.vm.$nextTick().then(() => {
+          expect(localStorage.getItem(storageKey)).toBe(String(newValue));
+        });
+      },
+    );
 
     it('does not save default value', () => {
       const value = 'ascending';
@@ -125,4 +127,88 @@ describe('Local Storage Sync', () => {
       });
     });
   });
+
+  describe('with "asJson" prop set to "true"', () => {
+    const storageKey = 'testStorageKey';
+
+    describe.each`
+      value             | serializedValue
+      ${null}           | ${'null'}
+      ${''}             | ${'""'}
+      ${true}           | ${'true'}
+      ${false}          | ${'false'}
+      ${42}             | ${'42'}
+      ${'42'}           | ${'"42"'}
+      ${'{ foo: '}      | ${'"{ foo: "'}
+      ${['test']}       | ${'["test"]'}
+      ${{ foo: 'bar' }} | ${'{"foo":"bar"}'}
+    `('given $value', ({ value, serializedValue }) => {
+      describe('is a new value', () => {
+        beforeEach(() => {
+          createComponent({
+            props: {
+              storageKey,
+              value: 'initial',
+              asJson: true,
+            },
+          });
+
+          wrapper.setProps({ value });
+
+          return wrapper.vm.$nextTick();
+        });
+
+        it('serializes the value correctly to localStorage', () => {
+          expect(localStorage.getItem(storageKey)).toBe(serializedValue);
+        });
+      });
+
+      describe('is already stored', () => {
+        beforeEach(() => {
+          localStorage.setItem(storageKey, serializedValue);
+
+          createComponent({
+            props: {
+              storageKey,
+              value: 'initial',
+              asJson: true,
+            },
+          });
+        });
+
+        it('emits an input event with the deserialized value', () => {
+          expect(wrapper.emitted('input')).toEqual([[value]]);
+        });
+      });
+    });
+
+    describe('with bad JSON in storage', () => {
+      const badJSON = '{ badJSON';
+
+      beforeEach(() => {
+        jest.spyOn(console, 'warn').mockImplementation();
+        localStorage.setItem(storageKey, badJSON);
+
+        createComponent({
+          props: {
+            storageKey,
+            value: 'initial',
+            asJson: true,
+          },
+        });
+      });
+
+      it('should console warn', () => {
+        // eslint-disable-next-line no-console
+        expect(console.warn).toHaveBeenCalledWith(
+          `[gitlab] Failed to deserialize value from localStorage (key=${storageKey})`,
+          badJSON,
+        );
+      });
+
+      it('should not emit an input event', () => {
+        expect(wrapper.emitted('input')).toBeUndefined();
+      });
+    });
+  });
 });