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var b = require('bonescript');
var led = ["USR0", "USR1", "USR2", "USR3"];
var state = [0, 0, 0, 0];

for (var i = 0; i < led.length; i++) {
    b.pinMode(led[i], 'out');
}

toggleLED = function() {
 state = state ? 0 : 1;
 b.digitalWrite(led, state);
};

timer = setInterval(toggleLED, 100);

stopTimer = function() {
 clearInterval(timer);
};

setTimeout(stopTimer, 3000);