[new] - Implement UnaryExpression extractor.

Will need for props that look like {!foo}.

Author: beefancohen

src/util/values/expressions/UnaryExpression.js

@@ -0,0 +1,23 @@
+import getValue from './index';
+
+const extract = value => {
+  const { operator, argument } = value;
+
+  switch (operator) {
+    case '-':
+      return -getValue(argument);
+    case '+':
+      return Number(getValue(argument));
+    case '!':
+      return !getValue(argument);
+    case '~':
+      return ~getValue(argument);
+    case 'typeof':
+    case 'delete':
+    case 'void':
+    default:
+      return undefined;
+  }
+};
+
+export default extract;

src/util/values/expressions/index.js

@@ -6,6 +6,7 @@ import FunctionExpression from './FunctionExpression';
 import LogicalExpression from './LogicalExpression';
 import MemberExpression from './MemberExpression';
 import CallExpression from './CallExpression';
+import UnaryExpression from './UnaryExpression';
 
 const TYPES = {
   Identifier,
@@ -15,7 +16,8 @@ const TYPES = {
   FunctionExpression,
   LogicalExpression,
   MemberExpression,
-  CallExpression
+  CallExpression,
+  UnaryExpression
 };
 
 const extract = value => {