Delays between promises in promise chain

Question

Let\'s say I am using the following code to run a couple of promises in series:

let paramerterArr = [\'a\',\'b\',\'c\',\'d\',\'e\',\'f\']
parameterArr.reduce         


        

Answer 1

since this seems to be a requirement of mySpecialFunction I'd implement it there. So that the function delays itself if it is called less than 50ms after the last call

const delayBetweenCalls = (delay, fn) => {
    let lastCall = NaN;
    return function(/*...arguments*/){
        //this and arguments are both forwarded to fn

        return new Promise(resolve => {
            let poll = () => {
                let delta = Date.now() - lastCall;
                if(delta < delay){
                    setTimeout(poll, delta - delay);
                }else{
                    lastCall = Date.now();
                    resolve( fn.apply(this, arguments) );
                }
            }
            poll();
        })
    }
}

then:

const mySpecialFunction = delayBetweenCalls(50, function(some, ...args){
    return someValueOrPromise;
});

//and your loop stays the same:
parameterArr.reduce(function(promise, item) {
    return promise.then(function(result) {
        return mySpecialFunction(item);
    })
}, Promise.resolve())

so it doesn't matter where/how mySpecialFunction is called, there will always be a delay of at least 50ms before it runs the code inside the passed callback.