According to the spec, "undefined" as the mapFn arg should not throw.

paulmillr · Sep 7, 2014 · 3ac0659 · 3ac0659 · cscott · Sep 10, 2014
1 parent 4218d77
commit 3ac0659
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diff --git a/es6-shim.js b/es6-shim.js
@@ -581,7 +581,7 @@
         var mapFn = arguments.length > 1 ? arguments[1] : undefined;
 
         var list = ES.ToObject(iterable, 'bad iterable');
-        if (arguments.length > 1 && !ES.IsCallable(mapFn)) {
+        if (mapFn !== undefined && !ES.IsCallable(mapFn)) {
           throw new TypeError('Array.from: when provided, the second argument must be a function');
         }
 

diff --git a/test/array.js b/test/array.js
@@ -160,8 +160,11 @@ var runArrayTests = function() {
         });
       });
 
+      it('does not throw when provided an undefined second arg', function() {
+        expect(Array.from([], undefined)).to.eql([]);
+      });
+
       it('throws when provided a nonfunction second arg', function() {
-        expect(function () { Array.from([], undefined); }).to.throw(TypeError);
         expect(function () { Array.from([], null); }).to.throw(TypeError);
         expect(function () { Array.from([], false); }).to.throw(TypeError);
         expect(function () { Array.from([], true); }).to.throw(TypeError);