javascript_add_property.md

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ADD PROPERTIES INTO JSON OBJECTS

JSON data is perfect for creating dependent items. However, sometimes the raw JSON is unprepared for processing. So, JavaScript preprocessing can be used to add new values or manipulate object properties. This can have some advantages depending on your scenario.

Possible benefits

• Manipulate data format;
• Add new properties;
• Calculate values before passing them to an LLD;
• Avoid creating a calculated item.

Syntax

var jsonValue = JSON.parse(value);
for (var i = 0; i < jsonValue.length; i++) {
  [newValue] = [codeLogic];
  jsonValue[i].[property] = [newValue];
}
return JSON.stringify(jsonValue);

This code is a simple yet effective way to add properties from JSON objects. Remember to change the [newValue] = [codeLogic]; to your own code logic and values.
Where [property] is the new property (key name) to add into the JSON object, and [newValue] is the value of your new property.

Example

Consider a Zabbix item that collects a JSON array with properties that represent a process start time and end time.

Note

The actual collected value is passed to the JavaScript preprocessing step as a textual string.

1. Consider the sample value below.

Tip

Avoid prettifying the data while testing it with Zabbix JavaScript.

[
    {
    "endTime": "20240202101020",
    "startTime": "20240202101010"
    },
    {
    "endTime": "20240202101030",
    "startTime": "20240202101010"
    },
    {
    "endTime": "20240202100920",
    "startTime": "20240202101010"
    }
]

Zabbix passes the value as a string, i.e. the input value of the preprocessing step looks more like this:

[{"endTime":"20240202101020","startTime":"20240202101010"},{"endTime":"20240202101030","startTime":"20240202101010"},{"endTime":"20240202100920","startTime":"20240202101010"}]

2. In this example, the startTime and endTime can be used to calculate the execution time for each process.

Notice that this JSON has several objects that represent a system process. The objects do not have an execution time property. Therefore, by using a JavaScript preprocessing step, we can calculate this execution time using the startTime and endTime strings and add this new value to the object.

Let's use the proposed code and add a few operations to accomplish this task.

var regexStartTime = value.replace(/\"startTime\":\"(\d{4})(\d{2})(\d{2})(\d{2})(\d{2})(\d{2})\"/g, "\"startTime\":\"$3-$2-$1 $4:$5:$6\"");
var regexEndTime   = regexStartTime.replace(/\"endTime\":\"(\d{4})(\d{2})(\d{2})(\d{2})(\d{2})(\d{2})\"/g, "\"endTime\":\"$3-$2-$1 $4:$5:$6\"");

var jsonValue = JSON.parse(regexEndTime);
for (var i = 0; i < jsonValue.length; i++) {

  var startDate = new Date(jsonValue[i].startTime);
  var endDate   = new Date(jsonValue[i].endTime);

  var execTime = (endDate.getTime() - startDate.getTime()) / 1000;

  if (execTime < 0) { execTime = 0; }
  jsonValue[i].execTime = execTime;
}
return JSON.stringify(jsonValue);

Here's what each piece of the code does:

a. The code starts by using regular expressions to manipulate the passed value string. It replaces occurrences of startTime and endTime into a more readable format. It goes from YYYYMMDDHHmmss to YYYY-MM-DD HH:mm:ss.

b. Next, the modified string (regexEndTime) is parsed into a JavaScript object using JSON.parse(). The resulting object is stored in the jsonValue variable.

c. A loop iterates through each element in jsonValue.
For each element, it creates "Date" variables from the startTime and endTime values. Calculates the execution time (in seconds) as the difference between endTime and startTime. If the calculated execTime is negative, it sets it to 0. Finally, the execTime property is added to the jsonValue variable.

d. The code returns the modified jsonValue object as a JSON string using JSON.stringify().

3. The resulting value is a JSON string with the execTime property.

[
    {
    "endTime": "02-02-2024 10:10:20",
    "execTime": 10,
    "startTime": "02-02-2024 10:10:10"
    },
    {
    "endTime": "02-02-2024 10:10:30",
    "execTime": 20,
    "startTime": "02-02-2024 10:10:10"
    },
    {
    "endTime": "02-02-2024 10:09:20",
    "execTime": 0,
    "startTime": "02-02-2024 10:10:10"
    }
]

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