Better error message when normalize is missing.

src.ts/errors.ts

@@ -122,3 +122,13 @@ export function setCensorship(censorship: boolean, permanent?: boolean): void {
     _censorErrors = !!censorship;
     _permanentCensorErrors = !!permanent;
 }
+
+export function checkNormalize(): void {
+    try {
+        if (String.fromCharCode(0xe9).normalize('NFD') !== String.fromCharCode(0x65, 0x0301)) {
+            throw new Error('broken')
+        }
+    } catch (error) {
+        throwError('platform missing String.prototype.normalize', UNSUPPORTED_OPERATION, { operation: 'String.prototype.normalize' });
+    }
+}

src.ts/utils/hdnode.ts

@@ -201,6 +201,8 @@ export function mnemonicToSeed(mnemonic: string, password?: string): string {
 export function mnemonicToEntropy(mnemonic: string, wordlist?: Wordlist): string {
     if (!wordlist) { wordlist = langEn; }
 
+    errors.checkNormalize();
+        
     var words = wordlist.split(mnemonic);
     if ((words.length % 3) !== 0) { throw new Error('invalid mnemonic'); }
 

src.ts/utils/utf8.ts

@@ -1,7 +1,7 @@
 'use strict';
 
 import { HashZero } from '../constants';
-
+import { checkNormalize } from '../errors';
 import { arrayify, concat, hexlify } from './bytes';
 
 ///////////////////////////////
@@ -23,6 +23,7 @@ export enum UnicodeNormalizationForm {
 export function toUtf8Bytes(str: string, form: UnicodeNormalizationForm = UnicodeNormalizationForm.current): Uint8Array {
 
     if (form != UnicodeNormalizationForm.current) {
+        checkNormalize();
         str = str.normalize(form);
     }
 

src.ts/wordlists/lang-ja.ts

@@ -132,9 +132,7 @@ class LangJa extends Wordlist {
     }
 
     split(mnemonic: string): Array<string> {
-        if (!mnemonic.normalize) {
-            errors.throwError('Japanese is unsupported on this platform; missing String.prototype.normalize', errors.UNSUPPORTED_OPERATION, { operation: 'String.prototype.normalize' });
-        }
+        errors.checkNormalize();
         return mnemonic.split(/(?:\u3000| )+/g);
     }