scripting: Fix equal between undefined and empty string.

lib/scripting/vbs-helper.spec.ts

@@ -199,6 +199,8 @@ describe('The scripting VBS Helper', () => {
 		expect(vbsHelper.equals(undefined, new VbsUndefined())).to.equal(true);
 		expect(vbsHelper.equals(new VbsUndefined(), undefined)).to.equal(true);
 		expect(vbsHelper.equals(new VbsUndefined(), new VbsUndefined())).to.equal(true);
+		expect(vbsHelper.equals(new VbsUndefined(), '')).to.equal(true);
+		expect(vbsHelper.equals('', new VbsUndefined())).to.equal(true);
 	});
 
 	it('should compare not equal using "equals"', () => {

lib/scripting/vbs-helper.ts

@@ -131,18 +131,31 @@ export class VBSHelper {
 			return true;
 		}
 
+		const undef1 = typeof value1 === 'object' && value1.__isUndefined;
+		const undef2 = typeof value2 === 'object' && value2.__isUndefined;
+
 		// VbsUndefined == undefined
-		if (typeof value1 === 'object' && value1.__isUndefined && typeof value2 === 'undefined') {
+		if (undef1 && typeof value2 === 'undefined') {
 			return true;
 		}
 
 		// undefined == VbsUndefined
-		if (typeof value2 === 'object' && value2.__isUndefined && typeof value1 === 'undefined') {
+		if (typeof value1 === 'undefined' && undef2) {
 			return true;
 		}
 
 		// VbsUndefined == VbsUndefined
-		if (typeof value1 === 'object' && value1.__isUndefined && typeof value2 === 'object' && value2.__isUndefined) {
+		if (undef1 && undef2) {
+			return true;
+		}
+
+		// '' == VbsUndefined
+		if (undef1 && value2 === '') {
+			return true;
+		}
+
+		// VbsUndefined == ''
+		if (value1 === '' && undef2) {
 			return true;
 		}
 

lib/scripting/vbs-undefined.spec.ts

@@ -31,4 +31,10 @@ describe('The VBScript undefined handler', () => {
 		expect(() => undef == 1).not.to.throw();
 	});
 
+	it('should return "undefined" as string', () => {
+		const undef = new VbsUndefined() as unknown;
+		// tslint:disable-next-line:triple-equals
+		expect('' + undef).to.equal('undefined');
+	});
+
 });

lib/scripting/vbs-undefined.ts

@@ -33,6 +33,9 @@ export class VbsUndefined implements ProxyHandler<any> {
 	}
 
 	public get(target: any, p: string | number | symbol, receiver: any): any {
+		if (p === 'toString') {
+			return () => undefined;
+		}
 		if (typeof p === 'symbol' || ['valueOf', 'toString', 'inspect', '__errGet', '__errSet'].includes(p as string)) {
 			return Reflect.get(target, p);
 		}