It might be that it just needs a pulse? so digitalPulse(A0,1,100) for a 100ms pulse on A0.
It's possible that if you leave it powered all the time that's not good for it?
That page says the impedance is 550 ohms, so 3.3*1000/550 = 6mA when driven from the Espruino's 3.3v - so from that side of things you're ok.
However if it's inductive it might be trying to put some extra voltage into Espruino when turned on/off and it might be an idea to put some 'clamp' diodes across it. I don't suppose you have an oscilloscope you could check with?
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