Add OperationError error type

.babelrc

@@ -10,5 +10,10 @@
             "modules": false,
             "useBuiltIns": true
         }]
+    ],
+    "plugins": [
+        ["babel-plugin-transform-builtin-extend", {
+            "globals": ["Error"]
+        }]
     ]
 }

package.json

@@ -68,6 +68,7 @@
   },
   "dependencies": {
     "babel-polyfill": "^6.26.0",
+    "babel-plugin-transform-builtin-extend": "1.1.2",
     "bcryptjs": "^2.4.3",
     "bignumber.js": "^6.0.0",
     "bootstrap": "^3.3.7",

src/core/Recipe.mjs

@@ -8,6 +8,7 @@
 import OpModules from "./config/modules/OpModules";
 import OperationConfig from "./config/OperationConfig.json";
 import log from "loglevel";
+import OperationError from "./errors/OperationError";
 
 /**
  * The Recipe controls a list of Operations and the Dish they operate on.
@@ -175,18 +176,24 @@ class Recipe  {
                     dish.set(output, op.outputType);
                 }
             } catch (err) {
-                const e = typeof err == "string" ? { message: err } : err;
-
-                e.progress = i;
-                if (e.fileName) {
-                    e.displayStr = op.name + " - " + e.name + " in " +
-                        e.fileName + " on line " + e.lineNumber +
-                        ".<br><br>Message: " + (e.displayStr || e.message);
+                // print expected errors in output pane
+                if (err instanceof OperationError) {
+                    dish.set(err.message, "string");
+                    return i;
                 } else {
-                    e.displayStr = op.name + " - " + (e.displayStr || e.message);
+                    const e = typeof err == "string" ? { message: err } : err;
+
+                    e.progress = i;
+                    if (e.fileName) {
+                        e.displayStr = op.name + " - " + e.name + " in " +
+                            e.fileName + " on line " + e.lineNumber +
+                            ".<br><br>Message: " + (e.displayStr || e.message);
+                    } else {
+                        e.displayStr = op.name + " - " + (e.displayStr || e.message);
+                    }
+
+                    throw e;
                 }
-
-                throw e;
             }
         }
 

src/core/errors/OperationError.mjs

@@ -0,0 +1,20 @@
+/**
+ * Create custom error type for handling operation input errors.
+ * i.e. where the operation can handle the error and print a
+ * message to the screen.
+ */
+class OperationError extends Error {
+    /**
+     * Standard error constructor. Adds no new behaviour.
+     * @param args standard error args
+     */
+    constructor(...args) {
+        super(...args);
+
+        if (Error.captureStackTrace) {
+            Error.captureStackTrace(this, OperationError);
+        }
+    }
+}
+
+export default OperationError;

src/core/operations/CartesianProduct.mjs

@@ -5,6 +5,7 @@
  */
 
 import Operation from "../Operation";
+import OperationError from "../errors/OperationError";
 
 /**
  * Set cartesian product operation
@@ -44,7 +45,8 @@ class CartesianProduct extends Operation {
      */
     validateSampleNumbers(sets) {
         if (!sets || sets.length < 2) {
-            throw "Incorrect number of sets, perhaps you need to modify the sample delimiter or add more samples?";
+            throw new OperationError("Incorrect number of sets, perhaps you" +
+                " need to modify the sample delimiter or add more samples?");
         }
     }
 
@@ -54,16 +56,13 @@ class CartesianProduct extends Operation {
      * @param {string} input
      * @param {Object[]} args
      * @returns {string}
+     * @throws {OperationError}
      */
     run(input, args) {
         [this.sampleDelim, this.itemDelimiter] = args;
         const sets = input.split(this.sampleDelim);
 
-        try {
-            this.validateSampleNumbers(sets);
-        } catch (e) {
-            return e;
-        }
+        this.validateSampleNumbers(sets);
 
         return this.runCartesianProduct(...sets.map(s => s.split(this.itemDelimiter)));
     }

src/core/operations/SetDifference.mjs

@@ -5,6 +5,7 @@
  */
 
 import Operation from "../Operation";
+import OperationError from "../errors/OperationError";
 
 /**
  * Set Difference operation
@@ -44,7 +45,7 @@ class SetDifference extends Operation {
      */
     validateSampleNumbers(sets) {
         if (!sets || (sets.length !== 2)) {
-            throw "Incorrect number of sets, perhaps you need to modify the sample delimiter or add more samples?";
+            throw new OperationError("Incorrect number of sets, perhaps you need to modify the sample delimiter or add more samples?");
         }
     }
 
@@ -54,16 +55,13 @@ class SetDifference extends Operation {
      * @param {string} input
      * @param {Object[]} args
      * @returns {string}
+     * @throws {OperationError}
      */
     run(input, args) {
         [this.sampleDelim, this.itemDelimiter] = args;
         const sets = input.split(this.sampleDelim);
 
-        try {
-            this.validateSampleNumbers(sets);
-        } catch (e) {
-            return e;
-        }
+        this.validateSampleNumbers(sets);
 
         return this.runSetDifference(...sets.map(s => s.split(this.itemDelimiter)));
     }

src/core/operations/SetIntersection.mjs

@@ -5,6 +5,7 @@
  */
 
 import Operation from "../Operation";
+import OperationError from "../errors/OperationError";
 
 /**
  * Set Intersection operation
@@ -44,7 +45,7 @@ class SetIntersection extends Operation {
      */
     validateSampleNumbers(sets) {
         if (!sets || (sets.length !== 2)) {
-            throw "Incorrect number of sets, perhaps you need to modify the sample delimiter or add more samples?";
+            throw new OperationError("Incorrect number of sets, perhaps you need to modify the sample delimiter or add more samples?");
         }
     }
 
@@ -54,16 +55,13 @@ class SetIntersection extends Operation {
      * @param {string} input
      * @param {Object[]} args
      * @returns {string}
+     * @throws {OperationError}
      */
     run(input, args) {
         [this.sampleDelim, this.itemDelimiter] = args;
         const sets = input.split(this.sampleDelim);
 
-        try {
-            this.validateSampleNumbers(sets);
-        } catch (e) {
-            return e;
-        }
+        this.validateSampleNumbers(sets);
 
         return this.runIntersect(...sets.map(s => s.split(this.itemDelimiter)));
     }