self-assert / Assertion

Class: Assertion<ValueType>

Represents a validation rule in the problem domain.

An Assertion expresses a condition that must hold for a given value. These rules are defined using one or more predicate functions, added via require. The assertion is considered to "hold" when all the conditions evaluate to true.

See

• Requirements provides a list of built-in requirements.

Example

Basic usage

const integerGreaterThan42 = Assertion.requiring(
  "integer.greaterThan42",
  "A human-readable description",
  Requirements.and(Requirements.isInteger, Requirements.greaterThan(42))
);

console.log(integerGreaterThan42.doesHold(42)); // false
console.log(integerGreaterThan42.doesHold(42.1)); // false
console.log(integerGreaterThan42.doesHold(43)); // true

Extends

• Rule<boolean, ValueType>

Type Parameters

Type Parameter	Default type	Description
ValueType	any	The type of value this assertion applies to.

Creation

fromJson()

static fromJson(assertionAsJson): Assertion<any>

Parameters

Parameter	Type
assertionAsJson	RuleLabelAsJson

Returns

Assertion<any>

---

labeled()

static labeled<ValueType>(id, description): Assertion<ValueType>

Type Parameters

Type Parameter	Default type
ValueType	any

Parameters

Parameter	Type
id	string
description	string

Returns

Assertion<ValueType>

---

requiring()

static requiring<ValueType>(anId, aDescription, aCondition): Assertion<ValueType>

Creates a new assertion with the given id, description and requirement.

If the requirement does not depend on a value (i.e., a function with no parameters), the rule will be typed as Assertion<void>.

Type Parameters

Type Parameter	Default type
ValueType	any

Parameters

Parameter	Type
anId	string
aDescription	string
aCondition	(value) => boolean

Returns

Assertion<ValueType>

Examples

Without a value

/** Typed as Assertion<void> */
const systemIsReady = Assertion.requiring(
  "sys.ready",
  "System must be ready",
  () => isReady()
);

With a value

/** Typed as Assertion<number> */
const greaterThan18 = Assertion.requiring(
  "age.min",
  "Must be over 18",
  (age: number) => age > 18
);

Rule definition

require()

require(aConditionToBeMet): this

Adds a necessary requirement for the rule to hold.

Parameters

Parameter	Type
aConditionToBeMet	RuleRequirement<boolean, ValueType>

Returns

this

this for chaining

Example

Add a requirement for the rule to hold

const nameValid = Assertion.requiring(
  "customer.name.notBlank",
  "Name must not be blank",
  Requirements.isNotBlank
);
nameValid.require((name) => name !== "Johnny");

console.log(nameValid.hasFailed("")); // true
console.log(nameValid.hasFailed("Johnny")); // true
console.log(nameValid.doesHold("John")); // true

Inherited from

Rule.require

Rule evaluation

doesHold()

doesHold(value): boolean

Evaluates the requirements for the given value, and returns whether the rule holds or not.

Parameters

Parameter	Type
value	ValueType

Returns

boolean

Overrides

Rule.doesHold

---

hasFailed()

hasFailed(value): boolean

Opposite of doesHold

Parameters

Parameter	Type
value	ValueType

Returns

boolean

Overrides

Rule.hasFailed

---

mustHold()

mustHold(value): void

Evaluates the requirements for the given value. If any condition is not met, throws a RulesBroken exception.

Parameters

Parameter	Type
value	ValueType

Returns

void

Overrides

Rule.mustHold

---

collectFailureInto()

collectFailureInto(failed, value): void

Updates the list of failed assertions with its label if the rule has failed for the given value.

Parameters

Parameter	Type
failed	LabeledRule[]
value	ValueType

Returns

void

Overrides

Rule.collectFailureInto

---

evaluateFor()

evaluateFor(aValue): RuleEvaluation<boolean, ValueType>

Prepares a RuleEvaluation for the given value.

This is the same as new RuleEvaluation(rule, value).

Parameters

Parameter	Type
aValue	ValueType

Returns

RuleEvaluation<boolean, ValueType>

Example

const nameNotBlank = Assertion.requiring(
  "customer.name.notBlank",
  "Name must not be blank",
  Requirements.isNotBlank
);

const evaluation = nameNotBlank.evaluateFor("John");
console.log(evaluation.doesHold()); // true

Inherited from

Rule.evaluateFor

Labeling

isLabeledAs()

isLabeledAs(aBrokenRuleLabel): boolean

Checks if the assertion has the same id and description as the given one.

Parameters

Parameter	Type
aBrokenRuleLabel	LabeledRule

Returns

boolean

Inherited from

Rule.isLabeledAs

---

hasLabel()

hasLabel(anId, aDescription): boolean

Compare the id and description of the assertion with the given ones.

Parameters

Parameter	Type
anId	string
aDescription	string

Returns

boolean

Inherited from

Rule.hasLabel

---

hasDescription()

hasDescription(aDescription): boolean

Checks if the assertion has the given description.

Parameters

Parameter	Type
aDescription	string

Returns

boolean

Remarks

This method is used mostly for testing.

Inherited from

Rule.hasDescription

---

hasLabelId()

hasLabelId(anId): boolean

Compares the id of the assertion with the given one.

Parameters

Parameter	Type
anId	string

Returns

boolean

Inherited from

Rule.hasLabelId

---

getId()

getId(): string

Returns the label identifier.

Returns

string

Inherited from

Rule.getId

---

getDescription()

getDescription(): string

Returns

string

Inherited from

Rule.getDescription