promise 顺序执行

promise-sequence.js

// promise 和 reduce 

(function() {

function sequenceTasks(tasks) {
    function recordValue(results, value) {
        results.push(value);
        return results;
    }
    var pushValue = recordValue.bind(null, []);
    return tasks.reduce(function(promise, task) {
        return promise.then(task).then(pushValue)
    }, Promise.resolve())
}

function randomNum(min, max) {
    return Math.floor(Math.random() * (max - min) + min); 
}

function upload(file) {
    return new Promise(function(resolve, reject) {
        console.log('handle - ' + file)
        setTimeout(function() {
            if(randomNum(1000, 2000) % 2 === 0) {
                resolve(file + ' - success')
            } else {
                reject(file + ' - fail');
            }
        }, randomNum(1000, 2000))
    })
}

function main() {
    var tasks = [];
    function task(f) {
        return upload(f).catch(function(err) {
            return err
        })
    }
    for(var i = 0; i < 5; i++) {
        tasks.push(
            task.bind(null, i)
        )
    }
    return sequenceTasks(tasks)
}

main().then(function(value) {
    console.log(value)
})
.catch(function(err) {
    console.log(err)
})

})()