refactor!: return a marker string to help Flow detect bad input

packages/field-base/src/input-mixin.d.ts

@@ -68,6 +68,4 @@ export declare class InputMixinClass {
   protected _toggleHasValue(hasValue: boolean): void;
 
   protected _valueChanged(value?: string, oldValue?: string): void;
-
-  protected _setHasInputValue(event: InputEvent): void;
 }

packages/field-base/src/input-mixin.js

@@ -206,7 +206,7 @@ export const InputMixin = dedupingMixin(
        * @private
        */
       __onInput(event) {
-        this._setHasInputValue(event);
+        this._hasInputValue = !!this._inputElementValue;
         this._onInput(event);
       }
 
@@ -267,19 +267,5 @@ export const InputMixin = dedupingMixin(
         // Setting a value programmatically, sync it to input element.
         this._forwardInputValue(newVal);
       }
-
-      /**
-       * Sets the `_hasInputValue` property based on the `input` event.
-       *
-       * @param {InputEvent} event
-       * @protected
-       */
-      _setHasInputValue(event) {
-        // In the case a custom web component is passed as `inputElement`,
-        // the actual native input element, on which the event occurred,
-        // can be inside shadow trees.
-        const target = event.composedPath()[0];
-        this._hasInputValue = target.value.length > 0;
-      }
     },
 );

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

@@ -9,6 +9,15 @@ import { InputController } from '@vaadin/field-base/src/input-controller.js';
 import { InputFieldMixin } from '@vaadin/field-base/src/input-field-mixin.js';
 import { LabelledInputController } from '@vaadin/field-base/src/labelled-input-controller.js';
 
+// [type=number] value returns an empty string for invalid numbers,
+// while valueAsNumber returns NaN for empty strings, which makes
+// invalid and empty values indistinguishable. It's only possible
+// to detect unparsable input by checking the validity.badInput
+// boolean property. This string is used in _inputElementValue
+// as a marker to help Flow detect and clear unparsable values
+// through that property.
+const BAD_INPUT_STRING = 'NaN';
+
 /**
  * A mixin providing common number field functionality.
  *
@@ -111,7 +120,7 @@ export const NumberFieldMixin = (superClass) =>
      * @private
      */
     get __hasUnparsableValue() {
-      return this.inputElement.validity.badInput;
+      return this._inputElementValue === BAD_INPUT_STRING;
     }
 
     /** @protected */
@@ -405,22 +414,6 @@ export const NumberFieldMixin = (superClass) =>
       super._onKeyDown(event);
     }
 
-    /**
-     * Native [type=number] inputs don't update their value
-     * when you are entering input that the browser is unable to parse
-     * e.g. "--5", hence we have to override this method from `InputMixin`
-     * so that, when value is empty, it would additionally check
-     * for bad input based on the native `validity.badInput` property.
-     *
-     * @param {InputEvent} event
-     * @protected
-     * @override
-     */
-    _setHasInputValue(event) {
-      const target = event.composedPath()[0];
-      this._hasInputValue = target.value.length > 0 || this.__hasUnparsableValue;
-    }
-
     /**
      * Override this method from `InputMixin` to prevent
      * the value change caused by user input from being treated
@@ -527,4 +520,18 @@ export const NumberFieldMixin = (superClass) =>
       this.__committedValue = this.value;
       this.__committedUnparsableValueStatus = this.__hasUnparsableValue;
     }
+
+    /** @override */
+    get _inputElementValue() {
+      if (this.inputElement && this.inputElement.validity.badInput) {
+        return BAD_INPUT_STRING;
+      }
+
+      return super._inputElementValue;
+    }
+
+    /** @override */
+    set _inputElementValue(value) {
+      super._inputElementValue = value;
+    }
   };