feat: add mnemonic strength (wevm#1618)

* feat: add mnemonic strength

* chore: run lint

* Update tough-tigers-compare.md

* Update tough-tigers-compare.md

---------

Co-authored-by: jxom <[email protected]>

.changeset/tough-tigers-compare.md

@@ -0,0 +1,5 @@
+---
+"viem": minor
+---
+
+Added `strength` parameter to `generateMnemonic`.

site/docs/accounts/mnemonic.md

@@ -58,6 +58,10 @@ import { english, generateMnemonic } from 'viem/accounts'
 const mnemonic = generateMnemonic(english)
 ```
 
+::: tip
+You can customize the strength of the generated mnemonic by passing a value between 128 and 256 as the second argument to the `generateMnemonic` function. This value must be a multiple of 32.
+:::
+
 Available wordlists:
 
 - `czech`

src/accounts/generateMnemonic.test.ts

@@ -51,3 +51,8 @@ test('traditionalChinese', () => {
   const phrase = generateMnemonic(traditionalChinese)
   expect(phrase.split(' ').length).toBe(12)
 })
+
+test('english 256 bits strength', () => {
+  const phrase = generateMnemonic(english, 256)
+  expect(phrase.split(' ').length).toBe(24)
+})

src/accounts/generateMnemonic.ts

@@ -7,9 +7,13 @@ export type GenerateMnemonicErrorType = ErrorType
  * @description Generates a random mnemonic phrase with a given wordlist.
  *
  * @param wordlist The wordlist to use for generating the mnemonic phrase.
+ * @param strength mnemonic strength 128-256 bits
  *
  * @returns A randomly generated mnemonic phrase.
  */
-export function generateMnemonic(wordlist: string[]): string {
-  return generateMnemonic_(wordlist)
+export function generateMnemonic(
+  wordlist: string[],
+  strength?: number,
+): string {
+  return generateMnemonic_(wordlist, strength)
 }