feat(scope): add scope field

Author: blond

lib/entity-name.js

@@ -156,6 +156,36 @@ class BemEntityName {
         return this._type;
     }
 
+    /**
+     * Returns scope of this entity.
+     *
+     * Important: block-typed entities has no scope.
+     *
+     * @example
+     * const BemEntityName = require('@bem/entity-name');
+     *
+     * const buttonName = new BemEntityName({ block: 'button' });
+     * const buttonTextName = new BemEntityName({ block: 'button', elem: 'text' });
+     * const buttonTextBoldName = new BemEntityName({ block: 'button', elem: 'text', mod: 'bold' });
+     *
+     * buttonName.scope;         // null
+     * buttonTextName.scope;     // BemEntityName { block: 'button' }
+     * buttonTextBoldName.scope; // BemEntityName { block: 'button', elem: 'elem' }
+     *
+     * @returns {BemEntityName} - scope entity name.
+     */
+    get scope() {
+        if (this.type === TYPES.BLOCK) { return null; }
+        if (this._scope) { return this._scope; }
+
+        this._scope = new BemEntityName({
+            block: this.block,
+            elem: this.type === TYPES.ELEM_MOD && this.elem
+        });
+
+        return this._scope;
+    }
+
     /**
      * Returns id for this entity.
      *
@@ -238,6 +268,7 @@ class BemEntityName {
      *
      * buttonTextName.belongsTo(buttonName); // true
      * buttonName.belongsTo(buttonTextName); // false
+     *
      * buttonTextBoldName.belongsTo(buttonTextName); // true
      * buttonTextBoldName.belongsTo(buttonName); // false
      *