Are arrays in JavaScript sparse?

Question | May 16, 2017 | nextptr 

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An element is added at [length+1] into array dinosaurs, which already has 2 elements in it:

var dinosaurs = ['Brontosaurus', 'Stegosaurus'];

dinosaurs[dinosaurs.length+1] = 'Tyrannosaurus';

What is the value of dinosaurs.length now?