feat(m4): add solution exe-004 letter-frequencies

projects/m4/004-letter-frequencies/js/exercise1.txt

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+Line 1: This is the first line.
+Line 2: This is the second line.
+Line 3: This is the third line.
+Line 4: This is the fourth line.
+Line 5: This is the fifth line.
+Line 6: This is the sixth line.
+Line 7: This is the seventh line.
+Line 8: This is the eighth line.
+Line 9: This is the ninth line.
+Line 10: This is the tenth line.
+Line 11: This is the eleventh line.
+Line 12: This is the twelfth line.
+Line 13: This is the thirteenth line.
+Line 14: This is the fourteenth line.
+Line 15: This is the fifteenth line.
+Line 16: This is the sixteenth line.
+Line 17: This is the seventeenth line.
+Line 18: This is the eighteenth line.
+Line 19: This is the nineteenth line.
+Line 20: This is the twentieth line.
+Line 21: This is the twenty-first line.
+Line 22: This is the twenty-second line.
+Line 23: This is the twenty-third line.
+Line 24: This is the twenty-fourth line.

projects/m4/004-letter-frequencies/js/index.js

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+const { error } = require('console');
+const { readFile } = require('fs/promises');
+
+let filePath = './exercise1.txt';
+
+readFile(filePath)
+    .then((data) => {
+        // Convert the string to an array replacing all characters that are not letters
+        let data1 = data
+            .toString()
+            .replace(/[0-9.,\/#!$%\^&\*;:{}=\-_`~(),' ', \r\n]/g, '')
+            .split('');
+
+        const count = {}; // It allows us to calculate the number of times a character in the file repeats or appears
+
+        data1.forEach((value) => {
+            const arr = count[value] ?? 0; // Nulling coalescing operator to start with 0 if count[value] is undefined or null
+            count[value] = arr + 1;
+        });
+
+        console.log(count);
+    })
+    .catch((error) => {
+        console.error('The program is unable to open the file you indicated');
+    });