crypto: expose ECDH class

For consistency with the rest of the crypto classes, exposes the ECDH
class. Originally, only the createECDH function was exposed, and there
was no real reason to hide the class.

Backport-PR-URL: #16245
PR-URL: #8188
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

lib/crypto.js

@@ -66,7 +66,6 @@ function toBuf(str, encoding) {
 }
 exports._toBuf = toBuf;
 
-
 const assert = require('assert');
 const StringDecoder = require('string_decoder').StringDecoder;
 
@@ -556,17 +555,16 @@ DiffieHellman.prototype.setPrivateKey = function setPrivateKey(key, encoding) {
 };
 
 
+exports.createECDH = exports.ECDH = ECDH;
 function ECDH(curve) {
+  if (!(this instanceof ECDH))
+    return new ECDH(curve);
   if (typeof curve !== 'string')
     throw new TypeError('"curve" argument should be a string');
 
   this._handle = new binding.ECDH(curve);
 }
 
-exports.createECDH = function createECDH(curve) {
-  return new ECDH(curve);
-};
-
 ECDH.prototype.computeSecret = DiffieHellman.prototype.computeSecret;
 ECDH.prototype.setPrivateKey = DiffieHellman.prototype.setPrivateKey;
 ECDH.prototype.setPublicKey = DiffieHellman.prototype.setPublicKey;

test/parallel/test-crypto-classes.js

@@ -18,6 +18,7 @@ const TEST_CASES = {
   'Verify': ['RSA-SHA1'],
   'DiffieHellman': [1024],
   'DiffieHellmanGroup': ['modp5'],
+  'ECDH': ['prime256v1'],
   'Credentials': []
 };