node.js Stream writable.end()用法及代碼示例

writable.end()方法是Stream模塊的內置應用程序編程接口，因此不再可以將更多數據寫入Writable。參數塊和編碼是可選的，這將允許在關閉流之前立即寫入一個最終的新數據塊。此外，可選的回調函數被添加為可寫流的“完成”事件的偵聽器。

用法:

writable.end( chunk, encoding, callback)

參數：此方法接受上述和以下所述的三個參數：

• chunk:它是要寫入的可選數據。塊的值必須是字符串，緩衝區或Uint8Array。對於對象模式，塊值可以是null以外的任何值。
• encoding:如果塊是字符串值，它將保存編碼值。
• callback:它是流的可選回調函數。

返回值：它返回在調用此方法之前寫入的數據，如果end()方法具有大量新數據，則該數據也將在最後返回。

以下示例說明了Node.js中writable.end()方法的使用：

範例1：

// Node.js program to demonstrate the      
// writable.end() method   
  
// INcluding stream module 
const stream = require('stream'); 
  
// Creating a stream and creating  
// a write function 
const writable = new stream.Writable({ 
  
  // Write function with its  
  // parameters 
  write:function(chunk, encoding, next) { 
  
    // Converting the chunk of 
    // data to string 
    console.log(chunk.toString()); 
    next(); 
  } 
}); 
  
// Writing data 
writable.write('hi'); 
  
// Calling end method with its  
// all the parameters 
writable.end("last data", "utf8", () => { 
     console.log("Writable stream ended!"); 
});

輸出：

hi
last data
Writable {
  _writableState:
   WritableState {
     objectMode:false,
     highWaterMark:16384,
     finalCalled:false,
     needDrain:false,
     ending:true,
     ended:true,
     finished:false,
     destroyed:false,
     decodeStrings:true,
     defaultEncoding:'utf8',
     length:0,
     writing:false,
     corked:0,
     sync:false,
     bufferProcessing:false,
     onwrite:[Function:bound onwrite],
     writecb:null,
     writelen:0,
     bufferedRequest:null,
     lastBufferedRequest:null,
     pendingcb:2,
     prefinished:true,
     errorEmitted:false,
     emitClose:true,
     autoDestroy:false,
     bufferedRequestCount:0,
     corkedRequestsFree:
      { next:null,
        entry:null,
        finish:[Function:bound onCorkedFinish] } },
  writable:false,
  _write:[Function:write],
  domain:null,
  _events:
   [Object:null prototype] {
     finish:{ [Function:bound onceWrapper] listener:[Function] } },
  _eventsCount:1,
  _maxListeners:undefined }
Writable stream ended!

範例2：

// Node.js program to demonstrate the      
// writable.end() method   
  
// INcluding stream module 
const stream = require('stream'); 
  
// Creating a stream and creating  
// a write function 
const writable = new stream.Writable({ 
  
  // Write function with its  
  // parameters 
  write:function(chunk, encoding, next) { 
  
    // Converting the chunk of 
    // data to string 
    console.log(chunk.toString()); 
    next(); 
  } 
}); 
  
// Writing data 
writable.write('hi'); 
  
// Calling end method with its  
// all the parameters 
writable.end("last data", "utf8", () => { 
     console.log("Writable stream ended!"); 
}); 
writable.write('GfG');

輸出：

hi
last data
Error [ERR_STREAM_WRITE_AFTER_END]:write after end
    at writeAfterEnd (_stream_writable.js:248:12)
    at Writable.write (_stream_writable.js:296:5)
    at /home/runner/LuxuriousLegitimateObservation/index.js:30:10
    at Script.runInContext (vm.js:133:20)
    at Object. (/run_dir/interp.js:156:20)
    at Module._compile (internal/modules/cjs/loader.js:778:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:789:10)
    at Module.load (internal/modules/cjs/loader.js:653:32)
    at tryModuleLoad (internal/modules/cjs/loader.js:593:12)
    at Function.Module._load (internal/modules/cjs/loader.js:585:3)Writab
le stream ended!

此處顯示錯誤，因為在end()方法之後調用了write()方法，這是不可能的。

參考： https://nodejs.org/api/stream.html#stream_writable_end_chunk_encoding_callback