An explanation of this kind of puzzle can be found on Wikipedia
Click on the path between two islands to build a bridge. Click the bridge to enhance it to a two-way bridge. Click the two-way bridge to make it go away.
I recommend the game Kulki as implemented by M. Terczyński
Fireworks provided by fireworks-js
Svg library provided by SVG.js
Shameless self-promotion of my blog
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