add CamelPascalToSnakeCase conversion

Author: 0APOCALYPSE0

Conversions/CamelPascalToSnakeCase.js

@@ -0,0 +1,41 @@
+/**
+ *  Transforms a camelCase (or PascalCase) string to snake_case
+ * @param {string} inputStr camelCase or PascalCase string
+ * @returns { string } snake_case string
+ */
+
+function camelPascalToSnakeCase(inputStr) {
+  if (typeof inputStr !== "string") {
+      throw new Error(`Expected string as input, found ${typeof inputStr}`);
+  }
+
+  let snakeStr = "";
+  let lastCharWasLower = false;
+
+  for (let index = 0; index < inputStr.length; index++) {
+      const char = inputStr[index];
+
+      if (/[A-Z]/.test(char) && (!lastCharWasLower || (index > 0 && /[a-z0-9]/.test(inputStr[index - 1])))) {
+          if (index > 0 && inputStr[index - 1] !== "_") {
+              snakeStr += "_";
+          }
+          snakeStr += char.toLowerCase();
+          lastCharWasLower = false;
+      } else if (/[a-z0-9]/.test(char)) {
+          snakeStr += char;
+          lastCharWasLower = /[a-z]/.test(char);
+      } else {
+          snakeStr += "_";
+          lastCharWasLower = false;
+      }
+  }
+
+  // Remove leading underscore
+  if (snakeStr[0] === "_") {
+      snakeStr = snakeStr.substring(1);
+  }
+
+  return snakeStr;
+}
+
+export { camelPascalToSnakeCase }

Conversions/test/CamelPascalToSnakeCase.test.js

@@ -0,0 +1,18 @@
+import { camelPascalToSnakeCase } from "../CamelPascalToSnakeCase";
+
+describe('camelToSnakeCase', () => {
+  it.each([
+    ['someRandomString', 'some_random_string'],
+    ['SomeRandomStr#ng', 'some_random_str_ng'],
+    ['123someRandom123String123', '123some_random123_string123'],
+    ['123SomeRandom123String123', '123_some_random123_string123'],
+    ['123SomeRandom123String123', '123_some_random123_string123'],
+    ['', ''],
+  ])('converts %s to snake_case %s', (input, expected) => {
+    expect(camelPascalToSnakeCase(input)).toBe(expected);
+  });
+
+  it('throws an error when the input is not a string', () => {
+    expect(() => camelPascalToSnakeCase(123)).toThrow('Expected string as input');
+  });
+});