Question

There is a var i, change value from 0 to 9 constantly and randomly; trigger function A only when i==1 for 200 milliseconds. Wondering if there are any functions to work this out?

Answer 1

You would need to use setTimeout^[MDN] to monitor the value of the variable. I would set the interval at 200ms and set a flag when the variable is the target value. If the variable is still the target value on the next interval, execute your function.

var i = 0;

function A() {
}

$(function() {
    var targetFlag = false,
        targetVal = 1,
        triggerA = function() {
            if (i == targetVal) {
                if (targetFlag) {
                    A();
                } else {
                    targetFlag = true;
                }
            } else {
                targetFlag = false;
            }

            setTimeout(triggerA, 200);
        };

    triggerA();
});