rspec/rules/S3403/javascript/rule.adoc

This rule raises an issue when a strict equality operator is used to compare objects of different types.

== Why is this an issue?

The strict equality operator in JavaScript is represented by three equal signs (``++===++``), the strict inequality with (``++!==++``). It is used to compare two values for equality, but with an important difference from the regular equality operator (``++==++``). The strict equality operator compares both value and type, while the regular equality operator only compares values after performing type coercion if necessary.

The problem with using the strict equality operator (``++===++``)  with operands of dissimilar types lies in the way JavaScript handles the comparison. When you use ``++===++`` to compare two values of different types, it will always return false since their types are different, regardless of whether the values could be considered equal under certain conditions.

=== Code examples

==== Noncompliant code example

[source,javascript,diff-id=1,diff-type=noncompliant]
----
let a = 8;
let b = "8";

if (a === b) { // Noncompliant: Always false since 'a' is a number and 'b' a string
  // ...
}
----

==== Compliant solution
To address this issue, you can use the loose equality operator (``++==++``), which performs type coercion.
[source,javascript,diff-id=1,diff-type=compliant]
----
let a = 8;
let b = "8";

if (a == b) {
  // ...
}
----

Alternatively, use the strict equality operator (``++===++``) but ensure that the operands have the same type before performing the comparison. You can explicitly convert the operands to a common type using functions like ``++Number()++``, ``++String()++``, or other appropriate methods depending on the situation.

[source,javascript,diff-id=1,diff-type=compliant]
----
let a = 8;
let b = "8";

if (a === Number(b)) {
  // ...
}
----

== Resources
=== Documentation

* MDN - https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Strict_equality[Strict equality (``++===++``)]
* MDN - https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Strict_inequality[Strict inequality (``++!==++``)]
* MDN - https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Equality[Equality (``++==++``)]
* MDN - https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Inequality[Inequality (``++!=++``)]
* MDN - https://developer.mozilla.org/en-US/docs/Glossary/Type_coercion[Type coercion]
* MDN - https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Number/Number[``++Number()++`` constructor]
* MDN - https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/String[``++String()++`` constructor]
* MDN - https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Boolean/Boolean[``++Boolean()++`` constructor]

ifdef::env-github,rspecator-view[]

'''
== Implementation Specification
(visible only on this page)

=== Message

Remove this ["==="|"!=="] check; it will always be [false|true]. Did you mean to use ["=="|"!="]?


include::../highlighting.adoc[]

'''
== Comments And Links
(visible only on this page)

include::../comments-and-links.adoc[]

endif::env-github,rspecator-view[]