support 'in' operator

__tests__/evaluate.spec.ts

@@ -1,5 +1,6 @@
 import evaluate, { registerFunction } from '../src';
 import { parseExpression, parse } from '@babel/parser';
+import { objectExpression } from '@babel/types';
 
 const context = {
   str: 'string',
@@ -115,8 +116,14 @@ describe('evaluate expression', () => {
     expect(evaluate('obj[obj.b.c]', context)).toEqual('ccc');
   });
 
-  it('str ? obj.a : 123', () => {
+  it('?  : ', () => {
     expect(evaluate('str ? obj.a : 123', context)).toEqual(1);
     expect(evaluate('!str ? obj.a : 123', context)).toEqual(123);
+  });
+
+  it('in operator', () => {
+    expect(evaluate('1 in arr', context)).toBeTruthy();
+    expect(evaluate('6 in arr', context)).toBeFalsy();
+    expect(evaluate('6 in undefined', context)).toBeFalsy();
   })
 });

package.json

@@ -1,6 +1,6 @@
 {
   "name": "ts-expression-evaluator",
-  "version": "1.3.9",
+  "version": "1.3.10",
   "description": "Context-based expression parse and evaluator.",
   "main": "build/main/index.js",
   "typings": "build/main/index.d.ts",

src/lib/Handlers.ts

@@ -42,6 +42,11 @@ export const Handlers: Handlers = {
           return evaluate(ast.left, context) < evaluate(ast.right, context);
         case '<=':
           return evaluate(ast.left, context) <= evaluate(ast.right, context);
+        case 'in': {
+          const container = evaluate(ast.right, context);
+          if (!container) return false;
+          return evaluate(ast.left, context) in container;
+        }
       }
     }
     throw new Error();