并发量控制

const mapLimit = (list, limit, asyncHandle) => {
	const recursion = (arr) => {
		return asyncHandle(arr.shift()).then((res) => {
			console.log('data', res);
			if (arr.length > 0) {
				return recursion(arr)
			}
			return 'finish'
		})
	}
	let asyncList = [];
	let listCopy = [].concat(list);
	while (limit--) {
		asyncList.push(recursion(listCopy))
	}
	return Promise.all(asyncList);
}

var dataLists = [1,2,3,4,5,6,7,8,9,11,100,123];
var count = 0;
mapLimit(dataLists, 3, (curItem)=>{
	return new Promise(resolve => {
		count++
		setTimeout(()=>{
			console.log(curItem, '当前并发量:', count--)
			resolve();
		}, Math.random() * 5000)
	});
}).then(response => {
	console.log('finish', response)
});

// limit = 5
while(limit--) {
	handleFunction(list)
}

let recursion = (arr) => {
	return asyncHandle(arr.shift())
		.then(()=>{
			// 迭代数组长度不为0， 递归执行自身
			if (arr.length!==0) return recursion(arr) 
			// 迭代数组长度为0，结束 
			else return 'finish';
		})
}

return Promise.all(allHandle)