Add mode to throw on invalid prop access, fixes #25

README.md

@@ -282,10 +282,12 @@ resolve and use that value!
 
 ### API
 
-#### mozjexl.Jexl
+#### mozjexl.Jexl(throwOnMissingProp)
 A reference to the Jexl constructor. To maintain separate instances of Jexl
 with each maintaining its own set of transforms, simply re-instantiate with
-`new mozjexl.Jexl()`.
+`new mozjexl.Jexl()`.  If `throwOnMissingProp` is set to `true`, the evaluator
+will throw an exception if an expression attempts to access a property that does
+not exist, otherwise it will silently continue.
 
 #### mozjexl.addBinaryOp(_{string} operator_, _{number} precedence_, _{function} fn_)
 Adds a binary operator to the Jexl instance. A binary operator is one that

lib/Jexl.js

@@ -14,10 +14,11 @@ var Evaluator = require("./evaluator/Evaluator"),
  * xpath-like drilldown into native Javascript objects.
  * @constructor
  */
-function Jexl() {
+function Jexl(throwOnMissingProp) {
   this._customGrammar = null;
   this._lexer = null;
   this._transforms = {};
+  this._throwOnMissingProp = throwOnMissingProp || true;
 }
 
 /**
@@ -175,7 +176,12 @@ Jexl.prototype._eval = function(exp, context) {
   var self = this,
     grammar = this._getGrammar(),
     parser = new Parser(grammar),
-    evaluator = new Evaluator(grammar, this._transforms, context);
+    evaluator = new Evaluator(
+      grammar,
+      this._transforms,
+      context,
+      this._throwOnMissingProp
+    );
   return Promise.resolve().then(function() {
     parser.addTokens(self._getLexer().tokenize(exp));
     return evaluator.eval(parser.complete());

lib/evaluator/Evaluator.js

@@ -35,11 +35,18 @@ var handlers = require("./handlers");
  *      to resolve the value of a relative identifier.
  * @constructor
  */
-var Evaluator = function(grammar, transforms, context, relativeContext) {
+var Evaluator = function(
+  grammar,
+  transforms,
+  context,
+  relativeContext,
+  throwOnMissingProp
+) {
   this._grammar = grammar;
   this._transforms = transforms || {};
   this._context = context || {};
   this._relContext = relativeContext || this._context;
+  this._throwOnMissingProp = throwOnMissingProp || false;
 };
 
 /**

lib/evaluator/handlers.js

@@ -81,16 +81,39 @@ exports.FilterExpression = function(ast) {
  * @private
  */
 exports.Identifier = function(ast) {
+  function contextHasProp(context, prop) {
+    return Object.prototype.hasOwnProperty.call(context, prop);
+  }
+
   if (ast.from) {
-    return this.eval(ast.from).then(function(context) {
+    return this.eval(ast.from).then(context => {
       if (Array.isArray(context)) context = context[0];
+
+      // XXX at some point, we should probably make an undefined context throw
+      // too.
       if (context === undefined) return undefined;
+
+      if (this._throwOnMissingProp && !contextHasProp(context, ast.value)) {
+        throw new Error(
+          `stemmed context does not have an identifier named ${ast.value}`
+        );
+      }
+
       return context[ast.value];
     });
   } else {
-    return ast.relative
-      ? this._relContext[ast.value]
-      : this._context[ast.value];
+    const contextToCheck = ast.relative ? this._relContext : this._context;
+
+    if (
+      this._throwOnMissingProp &&
+      !contextHasProp(contextToCheck, ast.value)
+    ) {
+      throw new Error(
+        `default context does not have an identifier named ${ast.value}`
+      );
+    }
+
+    return contextToCheck[ast.value];
   }
 };
 

test/evaluator/Evaluator-throw-on-missing-prop-mode.js

@@ -0,0 +1,210 @@
+/*
+ * Jexl
+ * Copyright (c) 2015 TechnologyAdvice,
+ * Copyright (c) 2022 Mozilla Foundation
+ */
+
+var chai = require("chai"),
+  chaiAsPromised = require("chai-as-promised"),
+  Lexer = require("../../lib/Lexer"),
+  Parser = require("../../lib/parser/Parser"),
+  Evaluator = require("../../lib/evaluator/Evaluator"),
+  grammar = require("../../lib/grammar").elements;
+
+chai.should();
+chai.use(chaiAsPromised);
+
+var lexer = new Lexer(grammar);
+
+function toTree(exp) {
+  var p = new Parser(grammar);
+  p.addTokens(lexer.tokenize(exp));
+  return p.complete();
+}
+
+// If you're adding a test to this file, you probably also want to add a
+// a corresponding test to Evaluator.js.
+
+describe("Evaluator in throwOnMissingProp mode", function() {
+  it("should evaluate an arithmetic expression", function() {
+    const e = new Evaluator(grammar, null, null, null, true);
+    return e.eval(toTree("(2 + 3) * 4")).should.become(20);
+  });
+  it("should evaluate a string concat", function() {
+    var e = new Evaluator(grammar, null, null, null, true);
+    return e
+      .eval(toTree('"Hello" + (4+4) + "Wo\\"rld"'))
+      .should.become('Hello8Wo"rld');
+  });
+  it("should evaluate a true comparison expression", function() {
+    var e = new Evaluator(grammar, null, null, null, true);
+    return e.eval(toTree("2 > 1")).should.become(true);
+  });
+  it("should evaluate a false comparison expression", function() {
+    var e = new Evaluator(grammar, null, null, null, true);
+    return e.eval(toTree("2 <= 1")).should.become(false);
+  });
+  it("should evaluate a complex expression", function() {
+    var e = new Evaluator(grammar, null, null, null, true);
+    return e
+      .eval(toTree('"foo" && 6 >= 6 && 0 + 1 && true'))
+      .should.become(true);
+  });
+  it("should evaluate an identifier chain", function() {
+    var context = { foo: { baz: { bar: "tek" } } },
+      e = new Evaluator(grammar, null, context, null, true);
+    return e.eval(toTree("foo.baz.bar")).should.become(context.foo.baz.bar);
+  });
+  it("should apply transforms", function() {
+    var context = { foo: 10 },
+      half = function(val) {
+        return val / 2;
+      },
+      e = new Evaluator(grammar, { half: half }, context, null, true);
+    return e.eval(toTree("foo|half + 3")).should.become(8);
+  });
+  it("should filter arrays", function() {
+    var context = {
+        foo: {
+          bar: [{ tek: "hello" }, { tek: "baz" }, { tok: "baz" }]
+        }
+      },
+      e = new Evaluator(grammar, null, context, null, true);
+    return e
+      .eval(toTree('foo.bar[.tek == "baz"]'))
+      .should.eventually.deep.equal([{ tek: "baz" }]);
+  });
+  it("should assume array index 0 when traversing", function() {
+    var context = {
+        foo: {
+          bar: [{ tek: { hello: "world" } }, { tek: { hello: "universe" } }]
+        }
+      },
+      e = new Evaluator(grammar, null, context, null, true);
+    return e.eval(toTree("foo.bar.tek.hello")).should.become("world");
+  });
+  it("should make array elements addressable by index", function() {
+    var context = {
+        foo: {
+          bar: [{ tek: "tok" }, { tek: "baz" }, { tek: "foz" }]
+        }
+      },
+      e = new Evaluator(grammar, null, context, null, true);
+    return e.eval(toTree("foo.bar[1].tek")).should.become("baz");
+  });
+  it("should allow filters to select object properties", function() {
+    var context = { foo: { baz: { bar: "tek" } } },
+      e = new Evaluator(grammar, null, context, null, true);
+    return e
+      .eval(toTree('foo["ba" + "z"].bar'))
+      .should.become(context.foo.baz.bar);
+  });
+  it("should reject simple filters on undefined objects", function() {
+    var context = { foo: {} },
+      e = new Evaluator(grammar, null, context, null, true);
+    return e.eval(toTree('foo.bar["baz"].tok')).should.be.rejected;
+  });
+  it("should reject complex filters on undefined objects", function() {
+    var context = { foo: {} },
+      e = new Evaluator(grammar, null, context, null, true);
+    return e.eval(toTree("foo.bar[.size > 1].baz")).should.be.rejected;
+  });
+  it("should throw when transform does not exist", function() {
+    var e = new Evaluator(grammar, null, null, null, true);
+    return e.eval(toTree('"hello"|world')).should.be.rejected;
+  });
+  it("should throw when top-level identifier doesn't exist", function() {
+    var context = { foo: { baz: { bar: "dog" } } },
+      e = new Evaluator(grammar, null, context, null, true);
+
+    return e.eval(toTree("monkey")).should.be.rejected;
+  });
+  it("should throw when child identifier doesn't exist", function() {
+    var context = { foo: { baz: { bar: "cat" } } },
+      e = new Evaluator(grammar, null, context, null, true);
+
+    return e.eval(toTree("foo.baz.monkey")).should.be.rejected;
+  });
+  it("should apply the DivFloor operator", function() {
+    var e = new Evaluator(grammar, null, null, null, true);
+    return e.eval(toTree("7 // 2")).should.become(3);
+  });
+  it("should evaluate an object literal", function() {
+    var e = new Evaluator(grammar, null, null, null, true);
+    return e
+      .eval(toTree('{foo: {bar: "tek"}}'))
+      .should.eventually.deep.equal({ foo: { bar: "tek" } });
+  });
+  it("should evaluate an empty object literal", function() {
+    var e = new Evaluator(grammar, null, null, null, true);
+    return e.eval(toTree("{}")).should.eventually.deep.equal({});
+  });
+  it("should evaluate a transform with multiple args", function() {
+    var e = new Evaluator(
+      grammar,
+      {
+        concat: function(val, a1, a2, a3) {
+          return val + ": " + a1 + a2 + a3;
+        }
+      },
+      null,
+      null,
+      true
+    );
+    return e
+      .eval(toTree('"foo"|concat("baz", "bar", "tek")'))
+      .should.become("foo: bazbartek");
+  });
+  it("should evaluate dot notation for object literals", function() {
+    var e = new Evaluator(grammar, null, null, null, true);
+    return e.eval(toTree('{foo: "bar"}.foo')).should.become("bar");
+  });
+  it("should allow access to literal properties", function() {
+    var e = new Evaluator(grammar, null, null, null, true);
+    return e.eval(toTree('"foo".length')).should.become(3);
+  });
+  it("should evaluate array literals", function() {
+    var e = new Evaluator(grammar, null, null, null, true);
+    return e
+      .eval(toTree('["foo", 1+2]'))
+      .should.eventually.deep.equal(["foo", 3]);
+  });
+  it("should allow properties on empty arrays", function() {
+    var context = { foo: {} },
+      e = new Evaluator(grammar, null, context, null, true);
+    return e.eval(toTree("[].baz")).should.become(undefined);
+  });
+  it('should apply the "in" operator to strings', function() {
+    var e = new Evaluator(grammar, null, null, null, true);
+    return Promise.all([
+      e.eval(toTree('"bar" in "foobartek"')).should.become(true),
+      e.eval(toTree('"baz" in "foobartek"')).should.become(false)
+    ]);
+  });
+  it('should apply the "in" operator to arrays', function() {
+    var e = new Evaluator(grammar, null, null, null, true);
+    return Promise.all([
+      e.eval(toTree('"bar" in ["foo","bar","tek"]')).should.become(true),
+      e.eval(toTree('"baz" in ["foo","bar","tek"]')).should.become(false)
+    ]);
+  });
+  it("should evaluate a conditional expression", function() {
+    var e = new Evaluator(grammar, null, null, null, true);
+    return Promise.all([
+      e.eval(toTree('"foo" ? 1 : 2')).should.become(1),
+      e.eval(toTree('"" ? 1 : 2')).should.become(2)
+    ]);
+  });
+  it("should allow missing consequent in ternary", function() {
+    var e = new Evaluator(grammar, null, null, null, true);
+    return e.eval(toTree('"foo" ?: "bar"')).should.become("foo");
+  });
+  it("does not treat falsey properties as undefined", function() {
+    const e = new Evaluator(grammar, null, null, null, true);
+    return e.eval(toTree('"".length')).should.become(0);
+  });
+  it("should handle an expression with arbitrary whitespace", function() {
+    var e = new Evaluator(grammar, null, null, null, true);
+    return e.eval(toTree("(\t2\n+\n3) *\n4\n\r\n")).should.become(20);
+  });
+});

test/evaluator/Evaluator.js

@@ -21,6 +21,9 @@ function toTree(exp) {
   return p.complete();
 }
 
+// If you're adding a test to this file, you probably also want to add a
+// a corresponding test to Evaluator-throw-on-missing-prop-mode.js.
+
 describe("Evaluator", function() {
   it("should evaluate an arithmetic expression", function() {
     const e = new Evaluator(grammar);
@@ -107,7 +110,7 @@ describe("Evaluator", function() {
   });
   it("should throw when transform does not exist", function() {
     var e = new Evaluator(grammar);
-    return e.eval(toTree('"hello"|world')).should.reject;
+    return e.eval(toTree('"hello"|world')).should.be.rejected;
   });
   it("should apply the DivFloor operator", function() {
     var e = new Evaluator(grammar);