例子

考慮有這樣的一個函數(shù)，這個函數(shù)會異步地連接到一個IPv4地址的TCP端口。我們通過例子來看文檔怎么寫：

/*
* Make a TCP connection to the given IPv4 address.  Arguments:
*
*    ip4addr        a string representing a valid IPv4 address
*
*    tcpPort        a positive integer representing a valid TCP port
*
*    timeout        a positive integer denoting the number of milliseconds
*                   to wait for a response from the remote server before
*                   considering the connection to have failed.
*
*    callback       invoked when the connection succeeds or fails.  Upon
*                   success, callback is invoked as callback(null, socket),
*                   where `socket` is a Node net.Socket object.  Upon failure,
*                   callback is invoked as callback(err) instead.
*
* This function may fail for several reasons:
*
*    SystemError    For "connection refused" and "host unreachable" and other
*                   errors returned by the connect(2) system call.  For these
*                   errors, err.errno will be set to the actual errno symbolic
*                   name.
*
*    TimeoutError   Emitted if "timeout" milliseconds elapse without
*                   successfully completing the connection.
*
* All errors will have the conventional "remoteIp" and "remotePort" properties.
* After any error, any socket that was created will be closed.
*/
function connect(ip4addr, tcpPort, timeout, callback)
{
assert.equal(typeof (ip4addr), 'string',
    "argument 'ip4addr' must be a string");
assert.ok(net.isIPv4(ip4addr),
    "argument 'ip4addr' must be a valid IPv4 address");
assert.equal(typeof (tcpPort), 'number',
    "argument 'tcpPort' must be a number");
assert.ok(!isNaN(tcpPort) && tcpPort > 0 && tcpPort < 65536,
    "argument 'tcpPort' must be a positive integer between 1 and 65535");
assert.equal(typeof (timeout), 'number',
    "argument 'timeout' must be a number");
assert.ok(!isNaN(timeout) && timeout > 0,
    "argument 'timeout' must be a positive integer");
assert.equal(typeof (callback), 'function');

/* do work */
}

這個例子在概念上很簡單，但是展示了上面我們所談?wù)摰囊恍┙ㄗh：

• 參數(shù)，類型以及其它一些約束被清晰的文檔化。

• 這個函數(shù)對于接受的參數(shù)是非常嚴(yán)格的，并且會在得到錯誤參數(shù)的時候拋出異常（程序員的失誤）。

• 可能出現(xiàn)的操作失敗集合被記錄了。通過不同的”name“值可以區(qū)分不同的異常，而”errno“被用來獲得系統(tǒng)錯誤的詳細(xì)信息。

• 異常被傳遞的方式也被記錄了（通過失敗時調(diào)用回調(diào)函數(shù)）。

• 返回的錯誤有”remoteIp“和”remotePort“字段，這樣用戶就可以定義自己的錯誤了（比如，一個HTTP客戶端的端口號是隱含的）。

• 雖然很明顯，但是連接失敗后的狀態(tài)也被清晰的記錄了：所有被打開的套接字此時已經(jīng)被關(guān)閉。

這看起來像是給一個很容易理解的函數(shù)寫了超過大部分人會寫的的超長注釋，但大部分函數(shù)實際上沒有這么容易理解。所有建議都應(yīng)該被有選擇的吸收，如果事情很簡單，你應(yīng)該自己做出判斷，但是記?。河檬昼姲杨A(yù)計發(fā)生的記錄下來可能之后會為你或其他人節(jié)省數(shù)個小時。