chapter 03: extracting a factory function that touches the filesystem and calling it

Author: devcorpio

chapter_03-using-stubs-to-break-dependencies/LogAn/fileExtensionManager.js

@@ -0,0 +1,38 @@
+const fs = require('fs');
+const util = require('util');
+
+const readFilePromisied = util.promisify(fs.readFile);
+
+function fileExtensionManager() {
+    /**
+     * @param {string} fileName
+     */
+    async function isValid(fileName) {
+        const fileNameExtensions = await readFilePromisied(
+            `${__dirname}/fileNameExtensions.config.json`,
+            'utf8'
+        ).then(fileContent => JSON.parse(fileContent).extensions);
+
+        const isValidExtension = fileNameExtensions.some(
+            function checkFileNameExtension(extension) {
+                if (
+                    fileName
+                        .toUpperCase()
+                        .endsWith(`.${extension.toUpperCase()}`)
+                ) {
+                    return true;
+                }
+
+                return false;
+            }
+        );
+
+        return isValidExtension;
+    }
+
+    return {
+        isValid,
+    };
+}
+
+module.exports = fileExtensionManager;

chapter_03-using-stubs-to-break-dependencies/LogAn/logAnalyzer.js

@@ -1,8 +1,7 @@
-const fs = require('fs');
-const util = require('util');
 const ArgumentError = require('./ArgumentError');
+const fileExtensionManagerFactory = require('./fileExtensionManager');
 
-const readFilePromisied = util.promisify(fs.readFile);
+const fileExtensionManager = fileExtensionManagerFactory();
 
 function logAnalyzer() {
     /**
@@ -28,7 +27,7 @@ function logAnalyzer() {
             throw new ArgumentError('filename has to be provided');
         }
 
-        const result = await isValid(fileName);
+        const result = await fileExtensionManager.isValid(fileName);
 
         if (!result) {
             return false;
@@ -38,32 +37,6 @@ function logAnalyzer() {
         return true;
     }
 
-    /**
-     * @param {string} fileName
-     */
-    async function isValid(fileName) {
-        const fileNameExtensions = await readFilePromisied(
-            `${__dirname}/fileNameExtensions.config.json`,
-            'utf8'
-        ).then(fileContent => JSON.parse(fileContent).extensions);
-
-        const isValidExtension = fileNameExtensions.some(
-            function checkFileNameExtension(extension) {
-                if (
-                    fileName
-                        .toUpperCase()
-                        .endsWith(`.${extension.toUpperCase()}`)
-                ) {
-                    return true;
-                }
-
-                return false;
-            }
-        );
-
-        return isValidExtension;
-    }
-
     return {
         getWasLastFileNameValid,
         isValidLogFileName,