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Dakota Sexton1,077 Points
I'm confused. Huston types 'circles', not 'circle', into the console. Shouldn't 'circle' always remain singular?
Steven Parker225,664 Points
He explains this is known as a "ghost selection" which is empty since there are (initially) no elements of that type. While his use of "circles" may have been accidental, if I understand what is happening he could potentially use ANY identifier that does not already exist.
Stephen Emery14,384 Points
You are right, the code he writes will fail. If you run 'viz.selectAll('circle') you will see the array he's talking about.