Add property "isEmpty" (#863)

* Add property isEmpty to State

* Update hovering menu example

* Document isEmpty

* Improve perf of isEmpty with @Soreine 's suggestion

* Fix return of isEmpty

docs/reference/models/state.md

@@ -33,6 +33,7 @@ For convenience, in addition to transforms, many of the [`Selection`](./selectio
   - [`isExpanded`](#isExpanded)
   - [`isFocused`](#isfocused)
   - [`isForward`](#isForward)
+  - [`isEmpty`](#isEmpty)
 - [Static Methods](#static-methods)
   - [`State.create`](#statecreate)
 - [Methods](#methods)
@@ -153,6 +154,10 @@ Whether the current selection is focused.
 
 Whether the current selection is forward.
 
+### `isEmpty`
+`Boolean`
+
+Whether the current selection is empty.
 
 ## Static Methods
 

examples/hovering-menu/index.js

@@ -179,7 +179,7 @@ class HoveringMenu extends React.Component {
     const { menu, state } = this.state
     if (!menu) return
 
-    if (state.isBlurred || state.isCollapsed) {
+    if (state.isBlurred || state.isEmpty) {
       menu.removeAttribute('style')
       return
     }

src/models/state.js

@@ -425,6 +425,26 @@ class State extends new Record(DEFAULTS) {
       : this.document.getTextsAtRange(this.selection)
   }
 
+  /**
+   * Check whether the selection is empty.
+   *
+   * @return {Boolean}
+   */
+
+  get isEmpty() {
+    const { startOffset, endOffset } = this
+
+    if (this.isCollapsed) {
+      return true
+    }
+
+    if (endOffset != 0 && startOffset != 0) {
+      return false
+    }
+
+    return this.fragment.text.length == 0
+  }
+
   /**
    * Return a new `Transform` with the current state as a starting point.
    *