js-asyc-promise-reading-summary

nested promise

  1. Request code:

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    const makeRequest = async() => {
    	const response = await fetch(url);
    	if(response.needAnotherRequest){
    		const secondResponse = await makeAnotherRequest(reponse);
    		console.log(secondResponse);
    		return secondResponse;
    	}
    	console.log(response);
    	return response;
    }

  2. sync a list post Request: 

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    let promise = Promise.resolve();
    let posts = [{}, {}, {}];

    posts.forEach(post => {
        //construct a new promise and replace the old one
        //promise return the resove callback
    	promise = promise.then(()=>{
    		return db.insert(post);
    	});
    });

    promise.then(()=>{
    	///all you post request has been make one by one
    });

if you want to make it concurrently post, it will looks like:

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posts.forEach(post=>{
	promise = promise.then(db.insert(post));
})

// this might not be correct.

sequential vs parallism

promise.all and yield all in generator as well as generate a list of promise and promise all of them immedieately