Add 3-read_file_async.js file

Author: Mar-Issah

0x05-Node_JS_basic/1-stdin.js

@@ -5,10 +5,9 @@ process.stdin.on('readable', () => {
 
   if (name.length > 0) {
     process.stdout.write(`Your name is: ${name}`);
-    process.exit();
   }
 });
 
-process.stdin.on('exit', () => {
+process.stdin.on('end', () => {
   process.stdout.write('This important software is now closing\n');
 });

0x05-Node_JS_basic/2-read_file.js

@@ -7,43 +7,42 @@ const fs = require('fs');
  */
 
 function countStudents(path) {
-  try {
-    const data = fs.readFileSync(path, 'utf8').split('\n');
+  if (!fs.existsSync(path)) {
+    throw new Error('Cannot load the database');
+  }
+  const data = fs.readFileSync(path, 'utf8').split('\n');
 
-    if (data.length === 0) {
-      throw new Error('Cannot load the database');
-    }
-    const students = data.map((line) => line.split(','));
+  if (data.length === 0) {
+    throw new Error('Cannot load the database');
+  }
+  const students = data.map((line) => line.split(','));
 
-    console.log(`Number of students: ${students.slice(1).length - 1}`);
+  console.log(`Number of students: ${students.slice(1).length - 1}`);
 
-    const fields = students[0];
-    const fieldIndex = fields.indexOf('field');
+  const fields = students[0];
+  const fieldIndex = fields.indexOf('field');
 
-    if (fieldIndex === -1) {
-      throw new Error('Field column not found');
-    }
+  if (fieldIndex === -1) {
+    throw new Error('Field column not found');
+  }
+
+  const validStudents = students
+    .slice(1)
+    .filter((student) => student[fieldIndex] !== undefined && student[fieldIndex] !== '');
 
-    const validStudents = students
-      .slice(1)
-      .filter((student) => student[fieldIndex] !== undefined && student[fieldIndex] !== '');
-
-    const classes = validStudents.reduce((acc, student) => {
-      const className = student[fieldIndex];
-      if (!acc[className]) {
-        acc[className] = [];
-      }
-      acc[className].push(student[fields.indexOf('firstname')]);
-      return acc;
-    }, {});
-
-    for (const [className, studentList] of Object.entries(classes)) {
-      console.log(`Number of students in ${className}: ${studentList.length}. List: ${studentList.join(', ')}`);
+  const classes = validStudents.reduce((acc, student) => {
+    const className = student[fieldIndex];
+    if (!acc[className]) {
+      acc[className] = [];
     }
-  } catch (error) {
-    console.error(error.message);
+    acc[className].push(student[fields.indexOf('firstname')]);
+    return acc;
+  }, {});
+
+  for (const [className, studentList] of Object.entries(classes)) {
+    console.log(`Number of students in ${className}: ${studentList.length}. List: ${studentList.join(', ')}`);
   }
 }
 
-countStudents('database.csv');
+// countStudents('database.csv');
 module.exports = countStudents;

0x05-Node_JS_basic/3-read_file_async.js

@@ -5,35 +5,39 @@ const fs = require('fs/promises');
  * @param {String} path - The path to the CSV data file.
  * @returns {Promise<void>}
  */
-const countStudents = async (path) => {
-  try {
-    const data = await fs.readFile(path, 'utf-8');
-    const fileLines = data.trim().split('\n');
-    const studentGroups = {};
-    const dbFieldNames = fileLines[0].split(',');
-    const studentPropNames = dbFieldNames.slice(0, -1);
 
-    fileLines.slice(1).forEach((line) => {
-      const [field, ...studentPropValues] = line.split(',');
-      studentGroups[field] = [
-        ...(studentGroups[field] || []),
-        Object.fromEntries(studentPropNames.map((propName, idx) => [propName, studentPropValues[idx]])),
-      ];
-    });
-
-    const totalStudents = Object.values(studentGroups).flat().length;
-    console.log(`Number of students: ${totalStudents}`);
+const countStudents = (path) =>
+  new Promise((resolve, reject) => {
+    fs.readFile(path, 'utf-8', (err, data) => {
+      if (err) {
+        reject(new Error('Cannot load the database'));
+      }
+      if (data) {
+        const fileLines = data.toString('utf-8').trim().split('\n');
+        const studentObj = {};
+        const fieldNames = fileLines[0].split(',');
+        const studentPropNames = fieldNames.slice(0, fieldNames.length - 1);
 
-    for (const [field, group] of Object.entries(studentGroups)) {
-      const studentNames = group.map((student) => student.firstname).join(', ');
-      console.log(`Number of students in ${field}: ${group.length}. List: ${studentNames}`);
-    }
+        for (const line of fileLines.slice(1)) {
+          const studentRow = line.split(',');
+          const studentPropValues = studentRow.slice(0, studentRow.length - 1);
+          const field = studentRow[studentRow.length - 1];
+          if (!Object.keys(studentObj).includes(field)) {
+            studentObj[field] = [];
+          }
+          const studentEntries = studentPropNames.map((propName, idx) => [propName, studentPropValues[idx]]);
+          studentObj[field].push(Object.fromEntries(studentEntries));
+        }
 
-    return true;
-  } catch (error) {
-    console.error('Cannot load the database');
-    throw error;
-  }
-};
+        const totalStudents = Object.values(studentObj).reduce((pre, cur) => (pre || []).length + cur.length);
+        console.log(`Number of students: ${totalStudents}`);
+        for (const [field, group] of Object.entries(studentObj)) {
+          const studentNames = group.map((student) => student.firstname).join(', ');
+          console.log(`Number of students in ${field}: ${group.length}. List: ${studentNames}`);
+        }
+        resolve(true);
+      }
+    });
+  });
 
 module.exports = countStudents;

0x05-Node_JS_basic/main.js

@@ -0,0 +1,11 @@
+const countStudents = require('./2-read_file.js');
+
+countStudents('nope.csv');
+//   .then(() => {
+//     console.log('Done!');
+//   })
+//   .catch((error) => {
+//     console.log(error);
+//   });
+
+//countStudents('database.csv');