object
fcf.type(
int|
string|
array[
int|
string|
object] a_type)
object
fcf.type(
object{
type, ...} a_description)
object
fcf.type(
int|
string|
array[
int|
string|
object] a_type,
object a_description)
Package: fcf-framework-core
File: fcf.js
Available from version: 2.0.16
Creates a type description object for subsequent validation and data building.
The function transforms the input parameter a_type (a string, a numeric type identifier, or an array of types) into a structured type object.
The resulting object includes validation rules (min, max, length, minLength, maxLength), conversion rules, default values, and the structure of nested elements for objects, arrays, iterables, and enums.
Arguments
int|string|array[int|string|object] a_type
- Type definition. It can be:
- A string (e.g., "string", "number", "array", "object", "enum").
- A numeric identifier (e.g., fcf.STRING, fcf.NUMBER).
- An array of types (to implement "one of many" logic). Can be specified by an object similar to the a_description argument, but in this case, this object must contain a type field of type int or string
object a_description
- If only the
a_description object is passed to the function, then it must have a
type field of type
int or
string.
Depending on the type, the a_description object may contain the following properties:
|
Parameter
|
Type
|
Applicable Types
|
Description
|
|
type
|
string|int
|
All
|
Mandatory definition of the base type
|
|
require
|
boolean
|
All
Used for arbitrary properties nested within an object (fcf.OBJECT)
|
If true, the absence of a value will trigger an error
|
|
convert
|
boolean
|
All
|
If true, the function attempts to cast a_value to the target type (e.g., string "10" to number 10).
|
|
default
|
mixed
|
All
|
The value returned if a_value is missing or does not match the type.
|
|
min
|
number
|
fcf.NUMBER
|
Sets the minimum acceptable value.
|
|
max
|
number
|
fcf.NUMBER
|
Sets the maximum acceptable value.
|
|
length
|
number
|
fcf.STRING
|
Strict match for the string length.
|
|
minLength
|
number
|
fcf.STRING
|
Strict the minimum length.
|
|
maxLength
|
number
|
fcf.STRING
|
Strict the maximum length.
|
|
item
|
number|string|object|array
|
fcf.ARRAY|fcf.ITERABLE|fcf.NUMBERED
|
Description of the type for elements within a collection
|
|
fields
|
object { FIELD_NAME: number|string|object|array }
|
fcf.OBJECT
|
Description of the type for elements within a collection
|
|
undeclared
|
undefined|true|false|number|string|object|array
|
fcf.OBJECT
|
Rules for fields not defined in fields.
Can be undefined. Ignore - All undeclared fields are simply ignored, that is, they do not end up in the resulting object.
Can be false. Disallow - If an undeclared field is encountered, an error is raised;
Can be true. Any type - All undeclared fields are included in the resulting object in their original form;
Can be number|string|object|array - Specific type object;
|
|
items
|
array
|
fcf.ENUM|fcf.SET
|
A list of allowed values
|
Result
object
- Returns the generated object with type information.
Example: Assembling values of type number
let fcf = require("fcf-framework-core");
let description = {
type: fcf.NUMBER,
};
let type = fcf.type(description);
let value = fcf.build(type, 1);
fcf.log.log("APP", value);
Output:
2026-05-22 21:20:41.824 [PID:6551] [LOG] [MOD:APP]: 1
Example: Assembly of an invalid value for the number type
let fcf = require("fcf-framework-core");
let description = {
type: fcf.NUMBER,
};
let type = fcf.type(description);
try {
let value = fcf.build(type, "1");
} catch (e){
fcf.log.err("APP", e.message);
}
Output:
2026-05-22 21:20:41.838 [PID:6551] [ERR] [MOD:APP]: The value passed does not match the specified types (number)
Example: An invalid value for the number type with conversion support
let fcf = require("fcf-framework-core");
let description = {
type: fcf.NUMBER,
convert: true,
};
let type = fcf.type(description);
let value = fcf.build(type, "1");
fcf.log.log("APP", value);
Output:
2026-05-22 21:20:41.838 [PID:6551] [LOG] [MOD:APP]: 1
Example: Constructing an enum value
let fcf = require("fcf-framework-core");
let description = {
type: fcf.ENUM,
items: ["none", "first", "second"],
};
let type = fcf.type(description);
let value = fcf.build(type, "none");
fcf.log.log("APP", value);
Output:
2026-05-22 21:20:41.839 [PID:6551] [LOG] [MOD:APP]: none
Example: Enum with default option
Example of constructing an enum value with substitution in case of a type mismatch.
let fcf = require("fcf-framework-core");
let description = {
type: fcf.ENUM,
items: ["none", "first", "second"],
default: "none" // We specify a default value.
// This value will be substituted in the
// event of a mismatch in the input data.
// In the event of an error, an exception is not thrown in the `build` method;
// instead, the value from the `default` property is substituted.
};
let type = fcf.type(description);
let value = fcf.build(type, "error_value");
fcf.log.log("APP", value);
Output:
2026-05-22 22:07:50.147 [PID:9977] [LOG] [MOD:APP]: none
Example: An enum value construction with exception handling
let fcf = require("fcf-framework-core");
let description = {
type: fcf.ENUM,
items: ["none", "first", "second"],
};
let type = fcf.type(description);
try {
let value = fcf.build(type, "error_value");
} catch (e){
fcf.log.err("APP", e.message);
}
Output:
2026-05-22 22:07:50.148 [PID:9977] [ERR] [MOD:APP]: The value passed does not match the specified types (enum["none";"first";"second"])
Example: Assembling a complex object with nested fields.
let fcf = require("fcf-framework-core");
let type = fcf.type("object",
{
fields: {
id: { type: "number", require: true }, // Mark these fields as required, indicating flag require = true.
tags: { type: "array", item: "string" },
settings: {
type: "object",
fields: {
active: { type: "boolean", default: true }
},
default: { active: true } // If this property was a mistake or it was absent, the default value is set.
}
},
undeclared: false // We prohibit the presence of unannounced fields in this structure.
}
);
let input = { id: 1, tags: ["admin", "user"] };
let result = fcf.build(type, input);
fcf.log.log("APP", "These settings fields are not passed:");
fcf.log.log("APP", result);
input = { id: 1, settings: { active: "error_value"} };
result = fcf.build(type, input);
fcf.log.log("APP", "Transmission of invalid data:");
fcf.log.log("APP", result);
input = { id: 1, tags: ["admin", "user"], settings: {active: false} };
result = fcf.build(type, input);
fcf.log.log("APP", "Transmission of valid data:");
fcf.log.log("APP", result);
Output:
2026-05-22 22:07:50.149 [PID:9977] [LOG] [MOD:APP]: These settings fields are not passed:
2026-05-22 22:07:50.149 [PID:9977] [LOG] [MOD:APP]: {
"id" : 1,
"tags" : [
"admin",
"user"
],
"settings" : {
"active" : true
}
}
2026-05-22 22:07:50.150 [PID:9977] [LOG] [MOD:APP]: Transmission of invalid data:
2026-05-22 22:07:50.150 [PID:9977] [LOG] [MOD:APP]: {
"id" : 1,
"settings" : {
"active" : true
}
}
2026-05-22 22:07:50.152 [PID:9977] [LOG] [MOD:APP]: Transmission of valid data:
2026-05-22 22:07:50.152 [PID:9977] [LOG] [MOD:APP]: {
"id" : 1,
"tags" : [
"admin",
"user"
],
"settings" : {
"active" : false
}
}
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