Justin's Words

AsyncJS 基础

Posted on | In |

AsyncJS 指的是 async，是一个异步处理的组件。

Series 和 Limit 的区别

  • Series - the same as but runs only a single async operation at a time
  • Limit - the same as but runs a maximum of limit async operations at a time

async.map

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var names = ['James', 'Kobe', 'Havard', 'Jermmy', 'Rondo'];

async.map(names, function(name, callback){
    callback(null, name.toUpperCase());
}, function(err, result) {
    if (err) return console.error(err);
    console.log(result);
});

输出：

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[ 'JAMES', 'KOBE', 'HAVARD', 'JERMMY', 'RONDO' ]

async. each

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async.each(names, function(name, callback) {
    console.log(name);
    if (typeof callback === 'function') callback();
},function(err) {
    console.log('done');
});

输出：

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James
Kobe
Havard
Jermmy
Rondo
done

async.eachSeries

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async.eachSeries(names, function(name, callback) {
    console.log(name);
    if (typeof callback === 'function') callback();
},function(err) {
    console.log('done');
}

输出：

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James
Kobe
Havard
Jermmy
Rondo
done

async.parallel

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async.parallel([function(callback) {
    console.log('yy');
    callback();
}, function(callback) {
    console.log('xx');
    callback();
}, function(callback) {
    console.log('dd');
    callback();
}], function() {
    console.log('done');
});

输出：

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yy
xx
dd
done

async.waterfall

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async.waterfall([function(callback) {
    console.log('yy');
    callback();
}, function(callback) {
    console.log('xx');
    callback();
}, function(callback) {
    console.log('dd');
    callback();
}], function() {
    console.log('done');
});

输出：

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yy
xx
dd
done

async.filterLimit

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async.filterLimit(names, 2, function(name, callback) {
    if (name === 'James') {
    callback(name);
    } else {
    callback();
    }
}, function(results) {
    console.log(results);
});

输出：

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[ 'James' ]

async.reject

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async.reject(names, function(name, callback) {
    if (name === 'James') {
    callback(name);
    } else {
    callback();
    }
}, function(results) {
    console.log(results);
});

输出:

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[ 'Kobe', 'Havard', 'Jermmy', 'Rondo' ]

async.reduce

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async.reduce([1, 2, 3, 4], 0, function(memo, num, callback) {
    callback(null, memo + num);
}, function(err, result) {
    console.log(result);
});

输出：

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10

async.every

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async.every(names, function(name, callback) {
    if (typeof name === 'string') {
    callback(true);
    } else {
    callback(false);
    }
}, function(result) {
    console.log(result);
});

输出：

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true

async.auto

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async.auto({
    get_data: function(callback){
        console.log('in get_data');
        // async code to get some data
        callback(null, 'data', 'converted to array');
    },
    make_folder: function(callback){
        console.log('in make_folder');
        // async code to create a directory to store a file in
        // this is run at the same time as getting the data
        callback(null, 'folder');
    },
    write_file: ['get_data', 'make_folder', function(callback, results){
        console.log('in write_file', JSON.stringify(results));
        // once there is some data and the directory exists,
        // write the data to a file in the directory
        callback(null, 'filename');
    }],
    email_link: ['write_file', function(callback, results){
        console.log('in email_link', JSON.stringify(results));
        // once the file is written let's email a link to it...
        // results.write_file contains the filename returned by write_file.
        callback(null, {'file':results.write_file, 'email':'user@example.com'});
    }]
}, function(err, results) {
    console.log('err = ', err);
    console.log('results = ', results);
});

输出：

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in get_data
in make_folder
in write_file {"get_data":["data","converted to array"],"make_folder":"folder"}
in email_link {"get_data":["data","converted to array"],"make_folder":"folder","write_file":"filename"}
err =  null
results =  { get_data: [ 'data', 'converted to array' ],
    make_folder: 'folder',
    write_file: 'filename',
    email_link: { file: 'filename', email: 'user@example.com' } }