feat: string helpers titleCase and isLetter

spec/string.spec.ts

@@ -1,4 +1,4 @@
-import { truncate, extractWords, camelCase, pascalCase } from '../src'
+import { truncate, extractWords, camelCase, pascalCase, titleCase, isLetter } from '../src'
 
 describe('truncate', () => {
     it('truncates string', () => {
@@ -37,3 +37,27 @@ describe('pascalCase', () => {
         expect(pascalCase('--foo1bar')).toEqual('Foo1Bar')
     })
 })
+
+describe('isLetter', () => {
+    it('checks if `a` is letter', () => {
+        expect(isLetter('a')).toBeTruthy()
+    })
+
+    it('checks if `-` is letter', () => {
+        expect(isLetter('-')).toBeFalsy()
+    })
+
+    it('checks if `Ž` is letter', () => {
+        expect(isLetter('Ž')).toBeTruthy()
+    })
+
+    it('checks if `9` is letter', () => {
+        expect(isLetter('9')).toBeFalsy()
+    })
+})
+
+describe('titleCase', () => {
+    it('changes string', () => {
+        expect(titleCase('hello-world FTW,abc999t t')).toEqual('Hello-World Ftw,Abc999T T')
+    })
+})

src/string.ts

@@ -48,6 +48,22 @@ export const octdigits = '01234567'
  */
 export const punctuation = '!"#$%&\'()*+,-./:;<=>?@[]^_`{|}~'
 
+/**
+ * Check if given value contains at least one letter.
+ *
+ * @example
+ * ```
+ * isLetter('a')
+ * // true
+* isLetter('-')
+ * // false
+ * ```
+ * @category String
+ */
+export function isLetter(value: string): boolean {
+    return value.toLowerCase() != value.toUpperCase()
+}
+
 /**
  * Truncates string
  *
@@ -118,3 +134,26 @@ export function pascalCase(value: string): string {
     const parsed = camelCase(value)
     return parsed.charAt(0).toUpperCase() + parsed.slice(1)
 }
+
+/**
+ * Convert the first letter in each to word upper case
+ *
+ * @example
+ * ```
+ * titleCase('hello world');
+ * // 'Hello World'
+ * ```
+ * @category String
+ */
+export function titleCase(value: string): string {
+    return value
+        .split('')
+        .map((char, index, chars) => {
+            const prevChar = chars[index - 1]
+            if (prevChar && isLetter(prevChar)) {
+                return char.toLowerCase()
+            }
+            return char.toUpperCase()
+        })
+        .join('')
+}