JS: Add extensibility point to supply a custom logging function

src/Framework/Framework/Resources/Scripts/dotvvm-root.ts

@@ -22,7 +22,7 @@ import * as api from './api/api'
 import * as eventHub from './api/eventHub'
 import * as viewModuleManager from './viewModules/viewModuleManager'
 import { notifyModuleLoaded } from './postback/resourceLoader'
-import { logError, logWarning, logInfo, logInfoVerbose, level, logPostBackScriptError } from "./utils/logging"
+import { logError, logWarning, logInfo, logInfoVerbose, level, logPostBackScriptError, setLogger } from "./utils/logging"
 import * as metadataHelper from './metadata/metadataHelper'
 import { StateManager } from "./state-manager"
 import { DotvvmEvent } from "./events"
@@ -119,7 +119,8 @@ const dotvvmExports = {
         logInfo,
         logInfoVerbose,
         logPostBackScriptError,
-        level
+        level,
+        setLogger
     },
     options,
     translations: translations as any,

src/Framework/Framework/Resources/Scripts/tests/validation.test.ts

@@ -2,6 +2,7 @@
 import { globalValidationObject as validation, ValidationErrorDescriptor } from "../validation/validation"
 import { createComplexObservableSubViewmodel, createComplexObservableViewmodel, ObservableHierarchy, ObservableSubHierarchy } from "./observableHierarchies"
 import { getErrors } from "../validation/error"
+import { setLogger } from "../utils/logging";
 
 
 describe("DotVVM.Validation - public API", () => {
@@ -139,6 +140,36 @@ describe("DotVVM.Validation - public API", () => {
         }
     })
 
+    test("addErrors - second level nonexistent property (setLogger capture)", () => {
+        //Setup
+        const vm = createComplexObservableViewmodel();
+        const logMessages: any[][] = []
+        let captureLog = true
+        setLogger((next, level, area, ...args) => {
+            if (captureLog && level == "warn")
+                logMessages.push([ "area", ...args ])
+            else
+                next(level, area, ...args)
+        })
+
+        try {
+            //Act
+            validation.addErrors(
+                [
+                    { errorMessage: "Does not matter", propertyPath: "/Prop1/NonExistent" },
+                ],
+                { root: ko.observable(vm) }
+            );
+
+            //Check
+            expect(logMessages.length).toBe(1);
+            expect(logMessages[0][1]).toContain("Validation error could not been applied to property specified by propertyPath /Prop1/NonExistent. Property with name NonExistent does not exist on /Prop1.");
+        }
+        finally {
+            captureLog = false
+        }
+    })
+
     test("addErrors - root level nonexistent property", () => {
         //Setup
         const vm = createComplexObservableViewmodel();

src/Framework/Framework/Resources/Scripts/utils/logging.ts

@@ -4,6 +4,28 @@ type LogLevel = "normal" | "verbose";
 
 export const level = getLogLevel();
 
+type ConsoleLogLevel = "warn" | "log" | "error" | "trace";
+
+let logger = function defaultLogger(level: ConsoleLogLevel, area: DotvvmLoggingArea, ...args: any) {
+    console[level](area, ...args)
+}
+
+/**
+ * Instead of calling console.log, console.warn or console.error, DotVVM will call this function instead.
+ * Please keep in mind that the exact wording of log messages is not DotVVM public API and may change without notice.
+ * @example
+ * dotvvm.log.setLogger((next, level, area, ...args) => {
+ *     if (area == "validation" && /^This message should be an error$/.test(args[0])) {
+ *          level = "error"
+ *     }
+*      previous(level, area, ...args) // call the default logger
+ * })
+ */
+export function setLogger(newLogger: (next: typeof logger, level: ConsoleLogLevel, area: DotvvmLoggingArea, ...args: any) => void) {
+    const nextLogger = logger;
+    logger = (...args) => newLogger(nextLogger, ...args);
+}
+
 export type DotvvmLoggingArea = (
     | "debug"
     | "configuration"
@@ -21,20 +43,20 @@ export type DotvvmLoggingArea = (
 
 export function logInfoVerbose(area: DotvvmLoggingArea, ...args: any[]) {
     if (compileConstants.debug && level === "verbose") {
-        console.log(area, ...args);
+        logger("log", area, ...args);
     }
 }
 
 export function logInfo(area: DotvvmLoggingArea, ...args: any[]) {
-    console.log(area, ...args);
+    logger("log", area, ...args);
 }
 
 export function logWarning(area: DotvvmLoggingArea, ...args: any[]) {
-    console.warn(area, ...args);
+    logger("warn", area, ...args);
 }
 
 export function logError(area: DotvvmLoggingArea, ...args: any[]) {
-    console.error(area, ...args);
+    logger("error", area, ...args);
 }
 
 export function logPostBackScriptError(err: any) {