buffer: make byteLength throw on invalid input

PR-URL: #8946
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Roman Reiss <me@silverwind.io>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Teddy Katz <teddy.katz@gmail.com>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Trevor Norris <trev.norris@gmail.com>

doc/api/buffer.md

@@ -631,8 +631,6 @@ console.log(`${str}: ${str.length} characters, ` +
 When `string` is a `Buffer`/[`DataView`]/[`TypedArray`]/[`ArrayBuffer`], the
 actual byte length is returned.
 
-Otherwise, converts to `String` and returns the byte length of string.
-
 ### Class Method: Buffer.compare(buf1, buf2)
 <!-- YAML
 added: v0.11.13

lib/buffer.js

@@ -369,7 +369,7 @@ function byteLength(string, encoding) {
       return string.byteLength;
     }
 
-    string = '' + string;
+    throw new TypeError('"string" must be a string, Buffer, or ArrayBuffer');
   }
 
   var len = string.length;

test/parallel/test-buffer-bytelength.js

@@ -7,10 +7,14 @@ const SlowBuffer = require('buffer').SlowBuffer;
 const vm = require('vm');
 
 // coerce values to string
-assert.strictEqual(Buffer.byteLength(32, 'latin1'), 2);
-assert.strictEqual(Buffer.byteLength(NaN, 'utf8'), 3);
-assert.strictEqual(Buffer.byteLength({}, 'latin1'), 15);
-assert.strictEqual(Buffer.byteLength(), 9);
+assert.throws(() => { Buffer.byteLength(32, 'latin1'); },
+              '"string" must be a string, Buffer, or ArrayBuffer');
+assert.throws(() => { Buffer.byteLength(NaN, 'utf8'); },
+              '"string" must be a string, Buffer, or ArrayBuffer');
+assert.throws(() => { Buffer.byteLength({}, 'latin1'); },
+              '"string" must be a string, Buffer, or ArrayBuffer');
+assert.throws(() => { Buffer.byteLength(); },
+              '"string" must be a string, Buffer, or ArrayBuffer');
 
 assert(ArrayBuffer.isView(new Buffer(10)));
 assert(ArrayBuffer.isView(new SlowBuffer(10)));