feat!: Throw custom errors instead of generics.

Changes errors into specific types so it's easier to determine what type
of error has occurred.

Author: nzakas

src/object-schema.js

@@ -62,9 +62,108 @@ function validateDefinition(name, strategy) {
     }
 }
 
+//-----------------------------------------------------------------------------
+// Errors
+//-----------------------------------------------------------------------------
+
+/**
+ * Error when an unexpected key is found.
+ */
+class UnexpectedKeyError extends Error {
+
+    /**
+     * Creates a new instance.
+     * @param {string} key The key that was unexpected. 
+     */
+    constructor(key) {
+        super(`Unexpected key "${key}" found.`);
+    }
+}
+
+/**
+ * Error when a required key is missing.
+ */
+class MissingKeyError extends Error {
+
+    /**
+     * Creates a new instance.
+     * @param {string} key The key that was missing. 
+     */
+    constructor(key) {
+        super(`Missing required key "${key}".`);
+    }
+}
+
+/**
+ * Error when a key requires other keys that are missing.
+ */
+class MissingDependentKeysError extends Error {
+
+    /**
+     * Creates a new instance.
+     * @param {string} key The key that was unexpected.
+     * @param {Array<string>} requiredKeys The keys that are required.
+     */
+    constructor(key, requiredKeys) {
+        super(`Key "${key}" requires keys "${requiredKeys.join("\", \"")}".`);
+    }
+}
+
+/**
+ * Wrapper error for errors occuring during a merge or validate operation.
+ */
+class WrapperError extends Error {
+
+    /**
+     * Creates a new instance.
+     * @param {string} key The object key causing the error. 
+     * @param {Error} source The source error. 
+     */
+    constructor(key, source) {
+        super(`Key "${key}": ` + source.message);
+
+        /**
+         * The original source error.
+         * @type {Error}
+         */
+        this.source = source;
+    }
+
+    /**
+     * The stack from the original error.
+     * @returns {string}
+     */
+    get stack() {
+        return this.source.stack;
+    }
+
+    /**
+     * The line number from the original error.
+     * @returns {number}
+     */
+    get lineNumber() {
+        return this.source.lineNumber;
+    }
+
+    /**
+     * The column number from the original error.
+     * @returns {number}
+     */
+    get columnNumber() {
+        return this.source.columnNumber;
+    }
+
+    /**
+     * The filename from the original error.
+     * @returns {string}
+     */
+    get fileName() {
+        return this.source.fileName;
+    }
+}
 
 //-----------------------------------------------------------------------------
-// Class
+// Main
 //-----------------------------------------------------------------------------
 
 /**
@@ -159,11 +258,11 @@ class ObjectSchema {
 
         // double check arguments
         if (objects.length < 2) {
-            throw new Error("merge() requires at least two arguments.");
+            throw new TypeError("merge() requires at least two arguments.");
         }
 
         if (objects.some(object => (object == null || typeof object !== "object"))) {
-            throw new Error("All arguments must be objects.");
+            throw new TypeError("All arguments must be objects.");
         }
 
         return objects.reduce((result, object) => {
@@ -179,8 +278,7 @@ class ObjectSchema {
                         }
                     }
                 } catch (ex) {
-                    ex.message = `Key "${key}": ` + ex.message;
-                    throw ex;
+                    throw new WrapperError(key, ex);
                 }
             }
             return result;
@@ -200,7 +298,7 @@ class ObjectSchema {
 
             // check to see if the key is defined
             if (!this.hasKey(key)) {
-                throw new Error(`Unexpected key "${key}" found.`);
+                throw new UnexpectedKeyError(key);
             }
 
             // validate existing keys
@@ -209,23 +307,22 @@ class ObjectSchema {
             // first check to see if any other keys are required
             if (Array.isArray(strategy.requires)) {
                 if (!strategy.requires.every(otherKey => otherKey in object)) {
-                    throw new Error(`Key "${key}" requires keys "${strategy.requires.join("\", \"")}".`);
+                    throw new MissingDependentKeysError(key, strategy.requires);
                 }
             }
 
             // now apply remaining validation strategy
             try {
                 strategy.validate.call(strategy, object[key]);
             } catch (ex) {
-                ex.message = `Key "${key}": ` + ex.message;
-                throw ex;
+                throw new WrapperError(key, ex);
             }
         }
 
         // ensure required keys aren't missing
         for (const [key] of this[requiredKeys]) {
             if (!(key in object)) {
-                throw new Error(`Missing required key "${key}".`);
+                throw new MissingKeyError(key);
             }
         }
 

tests/object-schema.js

@@ -110,6 +110,26 @@ describe("ObjectSchema", () => {
 
         });
 
+        it("should throw an error when merge() throws an error with a readonly message", () => {
+            let schema = new ObjectSchema({
+                foo: {
+                    merge() {
+                        throw {
+                            get message() {
+                                return "Boom!";
+                            }
+                        };
+                    },
+                    validate() {}
+                }
+            });
+
+            assert.throws(() => {
+                schema.merge({ foo: true }, { foo: true });
+            }, /Key "foo": Boom!/);
+        
+        });
+
         it("should call the merge() strategy for one key when called", () => {
 
             schema = new ObjectSchema({