一、目錄

1. 實驗目的

掌握函數(shù)節(jié)點的使用

2. 知識要點

• 函數(shù)節(jié)點在 node-red 中表示一個 JavaScript 函數(shù)塊，用來處理節(jié)點接收到的消息。
• 這些消息作為一個名為 msg 的 JavaScript 對象傳入。
• 通常有一個 msg.payload 屬性，包含消息正文。
• 函數(shù)被期望返回一個 message 對象（或多個消息對象），但是可以選擇不返回任何東西以阻止流。
• 發(fā)送消息：函數(shù)既可以使用“return”向流中的下一個節(jié)點傳遞消息，也可以調用 node.send（messages）。它可以返回或是發(fā)送
  　　　　一個單一的消息對象——傳遞給連接到第一個輸出的節(jié)點
  　　　　一組消息對象——傳遞給連接到相應輸出的節(jié)點
  　　如果數(shù)組的任何元素本身都是一組消息，那么多條消息就會被發(fā)送到相應的輸出。如果返回 null，無論是單獨還是作為數(shù)組的元素，都不會傳遞任何消息。要記錄任何信息或報告錯誤，可以使用以下功能：

node.log("Log message")
node.warn("Warning")
node.error("Error")

3. 實驗步驟

3.1 使用函數(shù)節(jié)點創(chuàng)建并返回多個信息

1. step1: 按照下圖組建流

1.實現(xiàn)

1.1 拖拽出四個節(jié)點。

2. step2: 修改其中的函數(shù)節(jié)點，使其具有兩個輸出口

2.實現(xiàn)

2.1 設置兩個輸出口

2.2 然后把節(jié)點連接起來

3. step3: 將以下代碼添加到函數(shù)節(jié)點

3.實現(xiàn)

3.1代碼添加到函數(shù)節(jié)點

代碼

var msg1 = {payload:"first out of output 1"};
var msg2 = {payload:"second out of output 1" };
var msg3 = {payload:"third out of output 1"} ;
var msg4 = { payload: "only message from output 2"} ;
return[[msg1, msg2, msg3],msg4] ;

4. step4: 部署，你在調試窗口看到了什么？

4.實現(xiàn)

4.1部署

4.2運行

image.png

5.實驗總結 第一個調試節(jié)點一口氣收到了 3 條消息，而第二個調試節(jié)點收到了一條消息，消息的內容跟剛剛輸入的代碼有關系，跟輸入的消息沒有任何關系，因為輸入的是時間戳。對比分析：

return msg ; //一 個 返 回 值
return [ [ msg1 , msg2 , msg3 ] , msg4 ] ; //一 組 返 回 值

3.2 通過判斷語句進行數(shù)據(jù)分類

         Switch 控件可以進行數(shù)據(jù)的分流，它屬于功能控件。函數(shù)控件是功能控件里，功能最強的，它可以實現(xiàn)switch 控件的功能。

1. step1: 按下圖組裝組件

注意這里 inject 節(jié)點輸入的是數(shù)字而不是時間戳，分別為 100,10,1

實現(xiàn)

1.拖拽節(jié)點

2.設置參數(shù)

剩余2個，重復以上操作即可

2. step2: 修改函數(shù)節(jié)點使其有 3 個輸出口

實現(xiàn)

1.設置參數(shù)，設置3 個輸出口

2.將所有的節(jié)點連接起來，如下圖

3. step3: 修改函數(shù)節(jié)點相關代碼，使其能夠進行分類判斷

if(msg.payload > 10)
{
    return [msg, null, null];
} else if(msg.payload === 10)
{
    return [null, msg, null];
} else
{
    return [null, null, msg];
}

實現(xiàn)

1.設置代碼

4. step4: 部署并調試，查看調試窗口

實現(xiàn)

5. step5: 試一試，按照字符串分類也是可以的

如果要求當檢測到第一個字符串”apple”，讓數(shù)據(jù)輸出在第一個輸出口 OUT1，當檢測到第二個字符串”banana”，讓數(shù)據(jù)輸出在第一個輸出口 OUT2，當檢測到第三個字符串”orange”，讓數(shù)據(jù)輸出在第一個輸出口 OUT3。您該如何修改程序？

實現(xiàn)

1.拖拽節(jié)點

2.設置節(jié)點

其余2個節(jié)點重復以上操作。

• 設置另一個節(jié)點配置，以及代碼

  
  
• 設置代碼如下圖

if (msg.payload == "apple") {
    return [msg, null, null];
} else if (msg.payload == "banana") {
    return [null, msg, null];
} else if (msg.payload == "orange") {
    return [null, null, msg];
}

再把所有節(jié)點連接起來，并部署，如下圖

3.3 單個數(shù)據(jù)計算

1. step1: 新建對象返回 拖入 inject 節(jié)點，并把輸入的內容改為數(shù)字；拖入 debug 節(jié)點用來觀察現(xiàn)象，拖入函數(shù)節(jié)點并做如下修改：

• 名稱設置為乘以 2
• 函數(shù)部分添加如下代碼：

var newMsg = {payload: msg.payload*2};
return newMsg;

其中，var newMsg = {payload: msg.payload * 2 } 語句的意思是，新建一個對象，名為 newMsg，它有 payload 屬性，并且 payload 的值為 msg.payload 的兩倍。最后返回的是 newMsg，也就是新建的這個對象。部署并運行，可以看到現(xiàn)象是，調試窗口顯示的數(shù)值是輸入的兩倍。說明函數(shù)節(jié)點的功能實現(xiàn)了。消息是通過 msg 對象傳過來的，可不可以不新建一個對象，直接修改 msg.payload 呢？

實現(xiàn)

1.拖入 inject 節(jié)點、并把輸入的內容改為數(shù)字

2.拖入 debug 節(jié)點用來觀察現(xiàn)象

3.拖入函數(shù)節(jié)點并做如下修改

4.部署并觀察數(shù)據(jù)變化

2. step2: 修改原有對象模式 將 step1 中的函數(shù)修改一下:

msg.payload = msg.payload*2;
return msg;

部署，可以發(fā)現(xiàn)結果一樣正確。

實現(xiàn)

1.部署與對比

3.4 使用數(shù)組進行數(shù)據(jù)截取與組裝

通常，在實際通信的時候不會只傳遞一個數(shù)組，信息的傳遞依賴于數(shù)組，數(shù)組中不同位置的數(shù)字也會有不同的含義，例如，第一個數(shù)字表示 ID，第二個數(shù)字表示數(shù)組長度，第三個數(shù)字表示溫度等等，一般會有一個通信協(xié)議來規(guī)定。所以，如何取出有用的數(shù)據(jù)，或者按要求把數(shù)據(jù)進行組裝很重要?，F(xiàn)在，假如收到了一串數(shù)據(jù)，數(shù)據(jù)共 16 位，我們只用到后 8 位，前邊的 8 位都不要了，如何來操作？

1. step1: 編輯 inject 節(jié)點 編輯 inject 節(jié)點使其輸入一組數(shù)組

實現(xiàn)

1.拖入節(jié)點，并連接

2.設置節(jié)點參數(shù)

[0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15]

2. step2: function 節(jié)點接入 inject 節(jié)點實現(xiàn)數(shù)據(jù)截斷

image.png

var temp = new Buffer([0, 0, 0, 0, 0, 0, 0, 0]);
for( var i = 0; i < 8; i++)
temp[i] = msg.payload[i + 8];
msg.payload = temp;
return msg;

實現(xiàn)

1.設置函數(shù)節(jié)點參數(shù)

3. step3: 部署運行，查看截斷的效果

實現(xiàn)

1.效果

3.5 模擬溫度數(shù)值計算

由于通信方式的限制，數(shù)據(jù)在發(fā)送時，常常要轉換為 8 位的字符來發(fā)送。在數(shù)字電路里，只有高電平和低電平兩種情況，所以數(shù)據(jù)在發(fā)送時，就只能使用 1 和 0 個數(shù)字。這個 1 或 0，稱之為 1 位。通常，8 位可以傳輸一個字符。2 的 8 次方是 256，所以小于 256 的數(shù)字，可以用 8 位來傳輸。而大于或等于 256 的數(shù)字，就要分成 2 個 8 位傳輸了。另外，8 位的數(shù)據(jù)可以用兩個十六進制的數(shù)來表示，比如 0101 1010 可以表示為 0x5a，所以通常會用十六進制來表示通信協(xié)議中的數(shù)。
　　例如，我們現(xiàn)在想傳輸十進制的數(shù)字 14859，大于 256，所以要分包傳送。十進制轉化為二進制是0011 1010 0000 1011，在通過硬件發(fā)送數(shù)據(jù)時，如果不考慮校驗或者起始位以及高位還是地位在前，就只考慮數(shù)字的發(fā)送，那么總線上的電平可能是低低高高，高低高低，低低低低，高低高高。把這個數(shù)字寫成十六進制，是 0x3a 與 0x0b，或 0x3a0b，0x 用來表示這是個十六進制的數(shù)字。0x3049 可以通過這種方式換算成 10 進制：數(shù)字拆成單個字符來分析，a 到 f 的數(shù)對應 10 到 15，在第幾位上，就乘以幾個 16。0x3a0b =3×16×16×16 ＋ 10×16×16 ＋ 11=14859?；蛘咧苯邮褂?16 進制進行計算，0x3a0b=0x3a×256+0x0b
　　當然，通信協(xié)議是可以進行特殊的規(guī)定，例如表示 4 位的溫度，34.56°C，要通過十六進制的數(shù)字進行分包發(fā)送，就是 0Xd80/100。我們現(xiàn)在規(guī)定，十六進制的溫度高位 ×256+ 低位 = 溫度 ×100。接下來嘗試解析溫度的數(shù)據(jù)。
　　我們使用 inject 節(jié)點輸入數(shù)組 [0xd,0x80]，由于 inject 節(jié)點里不支持直接輸入十六進制的數(shù)字，所以輸入 [13,128]。這兩個數(shù)組的值是一樣的。

1. step1: 使用 inject 節(jié)點模擬溫度數(shù)據(jù)輸入

實現(xiàn)

1.拖入節(jié)點，并連接

2.設置 inject 節(jié)點，參數(shù)

2. step2: 接入 function 節(jié)點并計算顯示的溫度數(shù)據(jù)值

image.png

實現(xiàn)

1.設置function 節(jié)點，參數(shù)代碼

var temp = (msg.payload[0] * 256 + msg.payload[1]) / 100;
msg.payload = temp;
return msg;

3. step3: 部署，運行，查看輸出

實現(xiàn)效果

全部代碼

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    {
        "id": "2285f598968b299e",
        "type": "tab",
        "label": "流程 3",
        "disabled": false,
        "info": "",
        "env": []
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    {
        "id": "fa937b8668055899",
        "type": "inject",
        "z": "2285f598968b299e",
        "name": "",
        "props": [
            {
                "p": "payload"
            },
            {
                "p": "topic",
                "vt": "str"
            }
        ],
        "repeat": "",
        "crontab": "",
        "once": false,
        "onceDelay": 0.1,
        "topic": "",
        "payload": "",
        "payloadType": "date",
        "x": 110,
        "y": 40,
        "wires": [
            [
                "7bddb6dd44a1f495"
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    {
        "id": "7bddb6dd44a1f495",
        "type": "function",
        "z": "2285f598968b299e",
        "name": "function 2",
        "func": "var msg1 = {payload:\"first out of output 1\"};\nvar msg2 = {payload:\"second out of output 1\" };\nvar msg3 = {payload:\"third out of output 1\"} ;\nvar msg4 = { payload: \"only message from output 2\"} ;\nreturn[[msg1, msg2, msg3],msg4] ;\n\n",
        "outputs": 2,
        "noerr": 0,
        "initialize": "",
        "finalize": "",
        "libs": [],
        "x": 280,
        "y": 40,
        "wires": [
            [
                "65d5e74df22c54e2"
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    },
    {
        "id": "65d5e74df22c54e2",
        "type": "debug",
        "z": "2285f598968b299e",
        "name": "debug 9",
        "active": true,
        "tosidebar": true,
        "console": false,
        "tostatus": false,
        "complete": "false",
        "statusVal": "",
        "statusType": "auto",
        "x": 440,
        "y": 20,
        "wires": []
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    {
        "id": "b593fe3dbbd92174",
        "type": "debug",
        "z": "2285f598968b299e",
        "name": "debug 10",
        "active": true,
        "tosidebar": true,
        "console": false,
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        "complete": "false",
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        "wires": []
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    {
        "id": "621d5293fa63f6e1",
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        "name": "function 3",
        "func": "if(msg.payload > 10)\n{\n    return [msg, null, null];\n} else if(msg.payload === 10)\n{\n    return [null, msg, null];\n} else\n{\n    return [null, null, msg];\n}\n",
        "outputs": 3,
        "noerr": 0,
        "initialize": "",
        "finalize": "",
        "libs": [],
        "x": 260,
        "y": 260,
        "wires": [
            [
                "4639173c87098450"
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        "name": "debug 11",
        "active": true,
        "tosidebar": true,
        "console": false,
        "tostatus": false,
        "complete": "false",
        "statusVal": "",
        "statusType": "auto",
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        "y": 180,
        "wires": []
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    {
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        "console": false,
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        "complete": "false",
        "statusVal": "",
        "statusType": "auto",
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        "wires": []
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    {
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        "type": "debug",
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        "name": "debug 13",
        "active": true,
        "tosidebar": true,
        "console": false,
        "tostatus": false,
        "complete": "false",
        "statusVal": "",
        "statusType": "auto",
        "x": 460,
        "y": 320,
        "wires": []
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    {
        "id": "e833aa26a5885270",
        "type": "inject",
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        "props": [
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            },
            {
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                "vt": "str"
            }
        ],
        "repeat": "",
        "crontab": "",
        "once": false,
        "onceDelay": 0.1,
        "topic": "",
        "payload": "100",
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        "type": "inject",
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        "props": [
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                "p": "topic",
                "vt": "str"
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        "repeat": "",
        "crontab": "",
        "once": false,
        "onceDelay": 0.1,
        "topic": "",
        "payload": "10",
        "payloadType": "num",
        "x": 110,
        "y": 260,
        "wires": [
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        "type": "inject",
        "z": "2285f598968b299e",
        "name": "",
        "props": [
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            {
                "p": "topic",
                "vt": "str"
            }
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        "repeat": "",
        "crontab": "",
        "once": false,
        "onceDelay": 0.1,
        "topic": "",
        "payload": "1",
        "payloadType": "num",
        "x": 110,
        "y": 300,
        "wires": [
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        "z": "2285f598968b299e",
        "name": "",
        "props": [
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                "p": "topic",
                "vt": "str"
            }
        ],
        "repeat": "",
        "crontab": "",
        "once": false,
        "onceDelay": 0.1,
        "topic": "",
        "payload": "apple",
        "payloadType": "str",
        "x": 110,
        "y": 440,
        "wires": [
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    {
        "id": "08ff10bdf4cef0df",
        "type": "inject",
        "z": "2285f598968b299e",
        "name": "",
        "props": [
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                "p": "payload"
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            {
                "p": "topic",
                "vt": "str"
            }
        ],
        "repeat": "",
        "crontab": "",
        "once": false,
        "onceDelay": 0.1,
        "topic": "",
        "payload": "banana",
        "payloadType": "str",
        "x": 110,
        "y": 480,
        "wires": [
            [
                "e55b0d9c5e4a1dbf"
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    },
    {
        "id": "05a89fc7b88cbf50",
        "type": "inject",
        "z": "2285f598968b299e",
        "name": "",
        "props": [
            {
                "p": "payload"
            },
            {
                "p": "topic",
                "vt": "str"
            }
        ],
        "repeat": "",
        "crontab": "",
        "once": false,
        "onceDelay": 0.1,
        "topic": "",
        "payload": "orange",
        "payloadType": "str",
        "x": 110,
        "y": 540,
        "wires": [
            [
                "e55b0d9c5e4a1dbf"
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    {
        "id": "e55b0d9c5e4a1dbf",
        "type": "function",
        "z": "2285f598968b299e",
        "name": "function 4",
        "func": "if (msg.payload == \"apple\") {\n    return [msg, null, null];\n} else if (msg.payload == \"banana\") {\n    return [null, msg, null];\n} else if (msg.payload == \"orange\") {\n    return [null, null, msg];\n}\n",
        "outputs": 3,
        "noerr": 0,
        "initialize": "",
        "finalize": "",
        "libs": [],
        "x": 260,
        "y": 480,
        "wires": [
            [
                "761f58e1183ae2b9"
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    {
        "id": "761f58e1183ae2b9",
        "type": "debug",
        "z": "2285f598968b299e",
        "name": "debug 14",
        "active": true,
        "tosidebar": true,
        "console": false,
        "tostatus": false,
        "complete": "payload",
        "targetType": "msg",
        "statusVal": "",
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