CamelPascalToSnakeCase conversion

Conversions/CamelPascalToSnakeCase.js

@@ -0,0 +1,44 @@
+/**
+ *  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 +1,21 @@
+import { camelPascalToSnakeCase } from '../CamelPascalToSnakeCase'
+
+describe('camelToSnakeCase', () => {
+  it.each([
+    ['someRandomString', 'some_random_string'],
+    ['SomeRandomStr#ng', 'some_random_str_ng'],
+    ['_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'
+    )
+  })
+})

DIRECTORY.md

@@ -41,6 +41,7 @@
   * [Base64ToArrayBuffer](Conversions/Base64ToArrayBuffer.js)
   * [BinaryToDecimal](Conversions/BinaryToDecimal.js)
   * [BinaryToHex](Conversions/BinaryToHex.js)
+  * [CamelPascalToSnakeCase](Conversions/CamelPascalToSnakeCase.js)
   * [DateDayDifference](Conversions/DateDayDifference.js)
   * [DateToDay](Conversions/DateToDay.js)
   * [DecimalToBinary](Conversions/DecimalToBinary.js)