JSON validation has been around for many years and there are quite a plethora of different javascript libraries out on git hub that can be used to validate your json payloads within your web apps. It came as a surprise to me that most people on the ServiceNow platform do not use a JSON validation library and instead opt to use a chain of if statements, chained functions, or simply wrap a section of code with a try catch block and call it a day. This can be a simple solution when you are working on an isolated feature, however can turn messy really quickly when you are trying to build a scalable solution. The beautiful part of ServiceNow is that almost every piece of data within the platform is served up in a JSON format and this is where JSON validators really shine.
Resources
- TV4 Json Schema Validator – https://github.com/geraintluff/tv4
- JSON Schema Generator – https://jsonschema.net/
- ServiceNow PDI – https://developer.servicenow.com
TV4
Tiny Validator v4 was actually picked for a couple of different reasons:
- Small package size
- Supports an industry standard schema format
- No modifications required to drop into ServiceNow
- Can be used in Script Includes
- Supports Async Validation
First we need to import tv4 into our ServiceNow instance to do this we will create a new script include and literally copy paste the library into the script include code section (yes its as easy as that).
https://github.com/geraintluff/tv4/blob/master/tv4.js <– TV4 code
JSON Schema
The payload we will be working with is as follows:
{
"checked": false,
"dimensions": {
"width": 5,
"height": 10
},
"id": 1,
"name": "A green door",
"price": 12.5,
"tags": [
"home",
"green"
]
}So in this payload all we care about is the id, price and tags. We will use the Generator tool to produce our schema
The schema that is generated is pretty straight forward
At the top layer we have a required key that tracks all required fields then each property has and $id, type, title and pattern which can be modified to meet your validation needs.
Generator Tool: https://jsonschema.net/
{
"definitions": {},
"$schema": "http://json-schema.org/draft-07/schema#",
"$id": "http://example.com/example.json",
"type": "object",
"title": "The Root Schema",
"required": [
"id",
"price",
"tags"
],
"properties": {
"checked": {
"$id": "/properties/checked",
"type": "boolean",
"title": "The Checked Schema",
"default": false,
"examples": [
false
]
},
"dimensions": {
"$id": "/properties/dimensions",
"type": "object",
"title": "The Dimensions Schema",
"required": [
"width",
"height"
],
"properties": {
"width": {
"$id": "/properties/dimensions/properties/width",
"type": "integer",
"title": "The Width Schema",
"default": 0,
"examples": [
5
]
},
"height": {
"$id": "/properties/dimensions/properties/height",
"type": "integer",
"title": "The Height Schema",
"default": 0,
"examples": [
10
]
}
}
},
"id": {
"$id": "/properties/id",
"type": "integer",
"title": "The Id Schema",
"default": 0,
"examples": [
1
]
},
"name": {
"$id": "/properties/name",
"type": "string",
"title": "The Name Schema",
"default": "",
"examples": [
"A green door"
],
"pattern": "^(.*)$"
},
"price": {
"$id": "/properties/price",
"type": "number",
"title": "The Price Schema",
"default": 0.0,
"examples": [
12.5
]
},
"tags": {
"$id": "/properties/tags",
"type": "array",
"title": "The Tags Schema",
"items": {
"$id": "/properties/tags/items",
"type": "string",
"title": "The 0 Schema",
"default": "",
"examples": [
"home",
"green"
],
"pattern": "^(.*)$"
}
}
}
}We will now take this JSON schema and save it in a new script include as a variable that is return when our function is called.
Validating a payload
Now to validate a payload take the following script as an example
var tv4 = new global.tv4();
var schemas = new global.schemas();
var payload = {
"checked": false,
"dimensions": {
"width": 5,
"height": 10
},
"id": 1,
"name": "A green door",
"price": 12.5
};
var result = tv4.validateMultiple(payload, schema.getDemoSchema());The result will show that our payload is invalid because the tags array is missing.
{
"valid": false,
"errors": [
{...},
...
],
"missing": [...]
}
