Custom error messages in JSON-Schema for Ajv validator
Please note
ajv-errors v3 supports ajv v8.
If you are using ajv v6, you should use ajv-errors v1
npm install ajv-errors
Add the keyword errorMessages to Ajv instance:
const Ajv = require("ajv").default
const ajv = new Ajv({allErrors: true})
// Ajv option allErrors is required
require("ajv-errors")(ajv /*, {singleError: true} */)See Options below.
Replace all errors in the current schema and subschemas with a single message:
const schema = {
type: "object",
required: ["foo"],
properties: {
foo: {type: "integer"},
},
additionalProperties: false,
errorMessage: "should be an object with an integer property foo only",
}
const validate = ajv.compile(schema)
console.log(validate({foo: "a", bar: 2})) // false
console.log(validate.errors) // processed errorsProcessed errors:
[
{
keyword: "errorMessage",
message: "should be an object with an integer property foo only",
// ...
params: {
errors: [
{keyword: "additionalProperties", instancePath: "" /* , ... */},
{keyword: "type", instancePath: ".foo" /* , ... */},
],
},
},
]Replace errors for certain keywords in the current schema only:
const schema = {
type: "object",
required: ["foo"],
properties: {
foo: {type: "integer"},
},
additionalProperties: false,
errorMessage: {
type: "should be an object", // will not replace internal "type" error for the property "foo"
required: "should have property foo",
additionalProperties: "should not have properties other than foo",
},
}
const validate = ajv.compile(schema)
console.log(validate({foo: "a", bar: 2})) // false
console.log(validate.errors) // processed errorsProcessed errors:
[
{
// original error
keyword: type,
instancePath: "/foo",
// ...
message: "should be integer",
},
{
// generated error
keyword: "errorMessage",
message: "should not have properties other than foo",
// ...
params: {
errors: [{keyword: "additionalProperties" /* , ... */}],
},
},
]For keywords "required" and "dependencies" it is possible to specify different messages for different properties:
const schema = {
type: "object",
required: ["foo", "bar"],
properties: {
foo: {type: "integer"},
bar: {type: "string"},
},
errorMessage: {
type: "should be an object", // will not replace internal "type" error for the property "foo"
required: {
foo: 'should have an integer property "foo"',
bar: 'should have a string property "bar"',
},
},
}Replace errors for properties / items (and deeper), regardless where in schema they were created:
const schema = {
type: "object",
required: ["foo", "bar"],
allOf: [
{
properties: {
foo: {type: "integer", minimum: 2},
bar: {type: "string", minLength: 2},
},
additionalProperties: false,
},
],
errorMessage: {
properties: {
foo: "data.foo should be integer >= 2",
bar: "data.bar should be string with length >= 2",
},
},
}
const validate = ajv.compile(schema)
console.log(validate({foo: 1, bar: "a"})) // false
console.log(validate.errors) // processed errorsProcessed errors:
[
{
keyword: "errorMessage",
message: "data.foo should be integer >= 2",
instancePath: "/foo",
// ...
params: {
errors: [{keyword: "minimum" /* , ... */}],
},
},
{
keyword: "errorMessage",
message: "data.bar should be string with length >= 2",
instancePath: "/bar",
// ...
params: {
errors: [{keyword: "minLength" /* , ... */}],
},
},
]When the value of keyword errorMessage is an object you can specify a message that will be used if any error appears that is not specified by keywords/properties/items using _ property:
const schema = {
type: "object",
required: ["foo", "bar"],
allOf: [
{
properties: {
foo: {type: "integer", minimum: 2},
bar: {type: "string", minLength: 2},
},
additionalProperties: false,
},
],
errorMessage: {
type: "data should be an object",
properties: {
foo: "data.foo should be integer >= 2",
bar: "data.bar should be string with length >= 2",
},
_: 'data should have properties "foo" and "bar" only',
},
}
const validate = ajv.compile(schema)
console.log(validate({})) // false
console.log(validate.errors) // processed errorsProcessed errors:
[
{
keyword: "errorMessage",
message: 'data should be an object with properties "foo" and "bar" only',
instancePath: "",
// ...
params: {
errors: [{keyword: "required" /* , ... */}, {keyword: "required" /* , ... */}],
},
},
]The message in property _ of errorMessage replaces the same errors that would have been replaced if errorMessage were a string.
Custom error messages used in errorMessage keyword can be templates using JSON-pointers or relative JSON-pointers to data being validated, in which case the value will be interpolated. Also see examples of relative JSON-pointers.
The syntax to interpolate a value is ${<pointer>}.
The values used in messages will be JSON-stringified:
- to differentiate between
falseand"false", etc. - to support structured values.
Example:
const schema = {
type: "object",
properties: {
size: {
type: "number",
minimum: 4,
},
},
errorMessage: {
properties: {
size: "size should be a number bigger or equal to 4, current value is ${/size}",
},
},
}Property names can be used in error messages with the relative JSON-pointer (e.g. 0#).
Example:
const schema = {
type: "object",
properties: {
size: {
type: "number",
},
},
additionalProperties: {
not: true,
errorMessage: βextra property is ${0#}β
}
}Defaults:
{
keepErrors: false,
singleError: false,
}- keepErrors: keep original errors. Default is to remove matched errors (they will still be available in
params.errorsproperty of generated error). If an error was matched and included in the error generated byerrorMessagekeyword it will have propertyemUsed: true. - singleError: create one error for all keywords used in
errorMessagekeyword (error messages defined for properties and items are not merged because they have different instancePaths). Multiple error messages are concatenated. Option values:false(default): create multiple errors, one for each messagetrue: create single error, messages are concatenated using"; "- non-empty string: this string is used as a separator to concatenate messages
ajv-errors package is a part of Tidelift enterprise subscription - it provides a centralised commercial support to open-source software users, in addition to the support provided by software maintainers.
To report a security vulnerability, please use the Tidelift security contact. Tidelift will coordinate the fix and disclosure. Please do NOT report security vulnerability via GitHub issues.