add isAlpha(…)

packages/tailwindcss/src/utils/is-alpha.bench.ts

@@ -0,0 +1,25 @@
+import { bench } from 'vitest'
+import { isAlpha } from './is-alpha'
+
+const ALPHA_REGEX_A = /^[a-zA-Z]+$/
+const ALPHA_REGEX_B = /^[a-z]+$/i
+const ALPHA_REGEX_C = /^[A-Z]+$/i
+
+const implementations = new Map<string, (input: string) => boolean>([
+  ['RegExp A', (input) => ALPHA_REGEX_A.test(input)],
+  ['RegExp B', (input) => ALPHA_REGEX_B.test(input)],
+  ['RegExp C', (input) => ALPHA_REGEX_C.test(input)],
+  ['Manual', isAlpha],
+])
+
+for (let [name, check] of implementations) {
+  bench(name, () => {
+    for (let i = 0; i < 1e6; i++) {
+      check('abc')
+      check('ABC')
+      check('AbC')
+      check('a-b-c')
+      check('123')
+    }
+  })
+}

packages/tailwindcss/src/utils/is-alpha.ts

@@ -0,0 +1,14 @@
+const UPPER_A = 65
+const UPPER_Z = 90
+const LOWER_A = 97
+const LOWER_Z = 122
+
+export function isAlpha(input: string): boolean {
+  for (let i = 0; i < input.length; i++) {
+    let code = input.charCodeAt(i)
+    if (code < UPPER_A || (code > UPPER_Z && code < LOWER_A) || code > LOWER_Z) {
+      return false
+    }
+  }
+  return true
+}