IconVault's Array Visualizer teaches JavaScript array methods the way a debugger would. Step through map, filter, reduce, find and sort one operation at a time while the index pointer moves across your array, each step explained in plain English, the result so far growing beside it and the accumulator shown for reduce.

Bring your own data (comma-separated values, up to 24 items) and even your own callback expression, which is compiled locally in your browser and never leaves your device. It is free with no signup. The honest framing: it builds real intuition for iteration, filtering and folding, which you then cement by writing the code yourself.