Adding unary operator + to transform string into numbers

src/ast.js

@@ -310,6 +310,7 @@ export class Binary extends Expression {
 
     // Null check for the operations.
     if (left == null || right == null) {
+
       switch (this.operation) {
         case '+':
           if (left != null) return left;
@@ -366,6 +367,24 @@ export class PrefixNot extends Expression {
   }
 }
 
+
+export class PrefixPlus extends Expression {
+  constructor(operation:string, expression:Expression){
+    super();
+
+    this.operation = operation;
+    this.expression = expression;
+  }
+
+  eval(scope, filters=defaultFilterMap){
+    return +this.expression.eval(scope);
+  }
+
+  accept(visitor){
+    visitor.visitPrefix(this);
+  }
+}
+
 export class LiteralPrimitive extends Expression {
   constructor(value){
     super();

src/parser.js

@@ -1,7 +1,7 @@
 import {Lexer,Token} from './lexer';
 import {Expression,ArrayOfExpression,Chain,Filter,Assign,
         Conditional, AccessScope, AccessMember, AccessKeyed, 
-        CallScope, CallFunction, CallMember, PrefixNot,
+        CallScope, CallFunction, CallMember, PrefixNot, PrefixPlus,
         Binary, LiteralPrimitive, LiteralArray, LiteralObject, LiteralString} from './ast';
 
 var EOF = new Token(-1, null);
@@ -205,7 +205,7 @@ export class ParserImplementation {
 
   parsePrefix():Expression {
     if (this.optional('+')) { 
-      return this.parsePrefix(); // TODO(kasperl): This is different than the original parser.
+      return new PrefixPlus('+', this.parsePrefix());
     } else if (this.optional('-')) {
       return new Binary('-', new LiteralPrimitive(0), this.parsePrefix());
     } else if (this.optional('!')) {

test/parser.spec.js

@@ -24,7 +24,12 @@ describe('parser', () => {
 
     it('should parse unary - expressions', () => {
       expect(evaluate("-1")).toEqual(-1);
+    });
+
+    it('should parse unary + expressions', () => {
       expect(evaluate("+1")).toEqual(1);
+      expect(evaluate("+'1'")).toEqual(1);
+      expect(evaluate("+'not a number'")).toEqual(NaN);
     });
 
     it('should parse unary ! expressions', () => {