fix: apply initially set custom field value to inputs

packages/custom-field/src/vaadin-custom-field-mixin.js

@@ -65,6 +65,7 @@ export const CustomFieldMixin = (superClass) =>
         inputs: {
           type: Array,
           readOnly: true,
+          observer: '__inputsChanged',
         },
 
         /**
@@ -249,7 +250,20 @@ export const CustomFieldMixin = (superClass) =>
     /** @private */
     __setInputsFromSlot() {
       this._setInputs(this.__getInputsFromSlot());
-      this.__setValue();
+    }
+
+    /** @private */
+    __inputsChanged(inputs, oldInputs) {
+      if (inputs.length === 0) {
+        return;
+      }
+
+      // When inputs are first initialized, apply value set with property.
+      if (this.value && this.value !== '\t' && (!oldInputs || oldInputs.length === 0)) {
+        this.__applyInputsValue(this.value);
+      } else {
+        this.__setValue();
+      }
     }
 
     /** @private */
@@ -265,18 +279,25 @@ export const CustomFieldMixin = (superClass) =>
         return;
       }
 
+      this.__applyInputsValue(value);
+
+      if (oldValue !== undefined) {
+        this.validate();
+      }
+    }
+
+    /** @private */
+    __applyInputsValue(value) {
       const parseFn = this.parseValue || defaultParseValue;
       const valuesArray = parseFn.apply(this, [value]);
+
       if (!valuesArray || valuesArray.length === 0) {
         console.warn('Value parser has not provided values array');
         return;
       }
 
-      this.inputs.forEach((input, id) => {
-        input.value = valuesArray[id];
+      this.inputs.forEach((input, idx) => {
+        input.value = valuesArray[idx];
       });
-      if (oldValue !== undefined) {
-        this.validate();
-      }
     }
   };

packages/custom-field/test/custom-field.common.js

@@ -79,6 +79,27 @@ describe('custom field', () => {
     });
   });
 
+  describe('value set with attribute', () => {
+    beforeEach(async () => {
+      customField = fixtureSync(`
+        <vaadin-custom-field value="01\t25">
+          <input type="number" />
+          <input type="number" />
+        </vaadin-custom-field>
+      `);
+      await nextRender();
+    });
+
+    it('should not reset value set using attribute', () => {
+      expect(customField.value).to.equal('01\t25');
+    });
+
+    it('should apply value set using attribute to inputs', () => {
+      expect(customField.inputs[0].value).to.equal('01');
+      expect(customField.inputs[1].value).to.equal('25');
+    });
+  });
+
   describe('aria-required', () => {
     it('should toggle aria-required attribute on required property change', async () => {
       customField.required = true;

test/integration/custom-field-lazy-inputs.test.js

@@ -0,0 +1,24 @@
+import { expect } from '@vaadin/chai-plugins';
+import { fixtureSync } from '@vaadin/testing-helpers';
+import '@vaadin/custom-field';
+
+describe('custom-field inputs', () => {
+  let customField;
+
+  beforeEach(async () => {
+    customField = fixtureSync(`
+      <vaadin-custom-field value="01\t25">
+        <vaadin-integer-field></vaadin-integer-field>
+        <vaadin-integer-field></vaadin-integer-field>
+      </vaadin-custom-field>
+    `);
+
+    // Ensure lazy custom element upgrade for slotted inputs.
+    await import('@vaadin/integer-field');
+  });
+
+  it('should apply value set using attribute to inputs', () => {
+    expect(customField.inputs[0].value).to.equal('01');
+    expect(customField.inputs[1].value).to.equal('25');
+  });
+});