Add distinguishable character set (#14)

Co-authored-by: Sindre Sorhus <sindresorhus@gmail.com>
sindresorhus · Mar 7, 2020 · c047603 · c047603
1 parent 9f45399
commit c047603
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Showing 4 changed files with 27 additions and 3 deletions.
diff --git a/index.d.ts b/index.d.ts
@@ -15,6 +15,8 @@ interface TypeOption {
 
 	@default 'hex'
 
+	The `distinguishable` set contains only uppercase characters that are not easily confused: `CDEHKMPRTUWXY012458`. It can be useful if you need to print out a short string that you'd like users to read and type back in with minimal errors. For example, reading a code off of a screen that needs to be typed into a phone to connect two devices.
+
 	@example
 	```
 	cryptoRandomString({length: 10});
@@ -28,9 +30,12 @@ interface TypeOption {
 
 	cryptoRandomString({length: 10, type: 'numeric'});
 	//=> '8314659141'
+
+	cryptoRandomString({length: 6, type: 'distinguishable'});
+	//=> 'CDEHKM'
 	```
 	*/
-	type?: 'hex' | 'base64' | 'url-safe' | 'numeric';
+	type?: 'hex' | 'base64' | 'url-safe' | 'numeric' | 'distinguishable';
 }
 
 interface CharactersOption {

diff --git a/index.js b/index.js
@@ -3,6 +3,7 @@ const crypto = require('crypto');
 
 const urlSafeCharacters = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789-._~'.split('');
 const numericCharacters = '0123456789'.split('');
+const distinguishableCharacters = 'CDEHKMPRTUWXY012458'.split('');
 
 const generateForCustomCharacters = (length, characters) => {
 	// Generating entropy is faster than complex math operations, so we use the simplest way
@@ -36,7 +37,8 @@ const allowedTypes = [
 	'hex',
 	'base64',
 	'url-safe',
-	'numeric'
+	'numeric',
+	'distinguishable'
 ];
 
 module.exports = ({length, type, characters}) => {
@@ -76,6 +78,10 @@ module.exports = ({length, type, characters}) => {
 		return generateForCustomCharacters(length, numericCharacters);
 	}
 
+	if (type === 'distinguishable') {
+		return generateForCustomCharacters(length, distinguishableCharacters);
+	}
+
 	if (characters.length === 0) {
 		throw new TypeError('Expected `characters` string length to be greater than or equal to 1');
 	}

diff --git a/readme.md b/readme.md
@@ -27,6 +27,9 @@ cryptoRandomString({length: 10, type: 'url-safe'});
 cryptoRandomString({length: 10, type: 'numeric'});
 //=> '8314659141'
 
+cryptoRandomString({length: 6, type: 'distinguishable'});
+//=> 'CDEHKM'
+
 cryptoRandomString({length: 10, characters: 'abc'});
 //=> 'abaaccabac'
 ```
@@ -52,12 +55,14 @@ Length of the returned string.
 
 Type: `string`\
 Default: `'hex'`\
-Values: `'hex' | 'base64' | 'url-safe' | 'numeric'`
+Values: `'hex' | 'base64' | 'url-safe' | 'numeric' | 'distinguishable'`
 
 Use only characters from a predefined set of allowed characters.
 
 Cannot be set at the same time as the `characters` option.
 
+The `distinguishable` set contains only uppercase characters that are not easily confused: `CDEHKMPRTUWXY012458`. It can be useful if you need to print out a short string that you'd like users to read and type back in with minimal errors. For example, reading a code off of a screen that needs to be typed into a phone to connect two devices.
+
 ##### characters
 
 Type: `string`\

diff --git a/test.js b/test.js
@@ -54,6 +54,14 @@ test('numeric', t => {
 	t.is(generatedCharacterSetSize({type: 'numeric'}, 10), 10);
 });
 
+test('distinquishable', t => {
+	t.is(cryptoRandomString({length: 0, type: 'distinguishable'}).length, 0);
+	t.is(cryptoRandomString({length: 10, type: 'distinguishable'}).length, 10);
+	t.is(cryptoRandomString({length: 100, type: 'distinguishable'}).length, 100);
+	t.regex(cryptoRandomString({length: 100, type: 'distinguishable'}), /^[CDEHKMPRTUWXY012458]*$/); // Sanity check, probabilistic
+	t.is(generatedCharacterSetSize({type: 'distinguishable'}, 19), 19);
+});
+
 test('characters', t => {
 	t.is(cryptoRandomString({length: 0, characters: '1234'}).length, 0);
 	t.is(cryptoRandomString({length: 10, characters: '1234'}).length, 10);