藍鳥承諾與事件發射器

Question

我對使用藍鳥承諾是相當新的。我試圖在發射器上使用它們。但是，我堅持如何處理錯誤。

我有一個stream對象，它是發射器。代碼如下 -

return new Promise((resolve, reject) => { 

    var onDocFunc = doc => { 
     //JSON.parse('*'); 
     // some logic goes in here to construct setStmt 
     bulk.find(query).upsert().update({$set: setStmt}); 
     count++; 
     if (count % bulkSize == 0) { 
      stream.pause(); 
      var execute = Promise.promisify(bulk.execute); 
      execute().catch(() => {}).then(() => { 
       stream.resume(); 
      }); 
     } 
    }; 

    stream.on('data', onDocFunc); 

    stream.on('end',() => { 
     JSON.parse('*'); // how to catch errors that happen here?? 
     var boundResolve = resolve.bind(this, {count: count}); 
     if (count % bulkSize != 0) { 
      Promise.promisify(bulk.execute)().then(boundResolve).catch(boundResolve); 
     } 
     else { 
      boundResolve(); 
     } 
    }); 

    stream.on('error', err => { 
     reject(err); 
    }); 

}) 

我想知道什麼是捕捉髮生在end事件處理程序的回調中的錯誤是推薦的方式？如果發生任何錯誤眼下，隨着uncaughtException: Unexpected token *

Answer 1

應用程序邏輯，不要混入事件發射的promisification。這樣的代碼（可以拋出等）應該總是在then回調。你的情況：

var execute = Promise.promisify(bulk.execute); 
return new Promise((resolve, reject) => { 
    stream.on('data', onDocFunc); // not sure what this does 
    stream.on('end', resolve); 
    stream.on('error', reject); 
}).then(() => { 
    JSON.parse('*'); // exceptions that happen here are caught implicitly! 
    var result = {count: count}; 
    if (count % bulkSize != 0) { 
     return execute().catch(()=>{}).return(result); 
    } else { 
     return result; 
    } 
}); 

---

關於你真正的代碼，我可能會嘗試分解出配料到一個輔助函數：

function asyncBatch(stream, size, callback) { 
    var batch = [], count = 0; 
    stream.on('data', data => { 
     batch.push(data); 
     count++; 
     if (batch.length == size) { 
      stream.pause(); 
      Promise.resolve(batch).then(callback).then(() => { 
       batch = []; 
       stream.resume(); 
      }, e => { 
       stream.emit('error', e); 
      }); 
     } 
    }); 
    return new Promise((resolve, reject) => { 
     stream.on('end', resolve); 
     stream.on('error', reject); 
    }).then(() => batch.length ? callback(batch) : null).then(() => count); 
} 

Promise.promisifyAll(Bulk); 
return asyncBatch(stream, bulkSize, docs => { 
    const bulk = new Bulk() 
    for (const doc of docs) { 
     // JSON.parse('*'); 
     // some logic goes in here to construct setStmt 
     bulk.find(query).upsert().update({$set: setStmt}); 
    } 
    return bulk.executeAsync().catch(err => {/* ignore */}); 
}) 

Answer 2

的應用程序的NodeJS崩潰你將不得不使用try/catch塊：

stream.on('end',() => { 
    try { 
    JSON.parse('*') 
    // ...the rest of your code 
    } catch (e) { 
    reject(e) 
    } 
})