Probably meant to be [].slice.call(document.querySelectorAll('.foo')).forEach(... It "casts" the NodeList which is "Array-like" to a proper Array, which h

Probably meant to be [].slice.call(document.querySelectorAll('.foo')).forEach(... It "casts" the NodeList which is "Array-like" to a proper Array, which has forEach, map and other useful methods in its prototype.