[New] add AssignmentExpression

Fixes #42

__tests__/src/getPropValue-babelparser-test.js

@@ -1046,6 +1046,26 @@ describe('getPropValue', () => {
     });
   });
 
+  describe('AssignmentExpression', () => {
+    it('should recognize and extract assignment', () => {
+      const prop = extractProp('<div foo={foo = bar} />');
+
+      const expected = 'foo = bar';
+      const actual = getPropValue(prop);
+
+      assert.deepEqual(actual, expected);
+    });
+
+    it('should recognize and extract combination assignments', () => {
+      const prop = extractProp('<div foo={foo += bar} />');
+
+      const expected = 'foo += bar';
+      const actual = getPropValue(prop);
+
+      assert.deepEqual(actual, expected);
+    });
+  });
+
   describeIfNotBabylon('Typescript', () => {
     beforeEach(() => {
       changePlugins((pls) => [...pls, 'typescript']);

src/values/expressions/AssignmentExpression.js

@@ -0,0 +1,13 @@
+/**
+ * Extractor function for a AssignmentExpression type value node.
+ * An assignment expression looks like `x = y` or `x += y` in expression position.
+ * This will return the assignment as the value.
+ *
+ * @param - value - AST Value object with type `AssignmentExpression`
+ * @returns - The extracted value converted to correct type.
+ */
+export default function extractValueFromAssignmentExpression(value) {
+  // eslint-disable-next-line global-require
+  const getValue = require('./index.js').default;
+  return `${getValue(value.left)} ${value.operator} ${getValue(value.right)}`;
+}

src/values/expressions/index.js

@@ -23,6 +23,7 @@ import SpreadElement from './SpreadElement';
 import TypeCastExpression from './TypeCastExpression';
 import SequenceExpression from './SequenceExpression';
 import TSNonNullExpression from './TSNonNullExpression';
+import AssignmentExpression from './AssignmentExpression';
 
 // Composition map of types to their extractor functions.
 const TYPES = {
@@ -52,6 +53,7 @@ const TYPES = {
   TypeCastExpression,
   SequenceExpression,
   TSNonNullExpression,
+  AssignmentExpression,
 };
 
 const noop = () => null;