rspec/rules/S1534/javascript/rule.adoc

== Why is this an issue?

JavaScript allows duplicate member names in classes and object literals, but only the last instance of a duplicated name determines the actual value that will be used for it. Therefore, changing values of other occurrences of a duplicated name will have no effect and may cause misunderstandings and bugs.


Defining a ``++class++`` with a duplicated ``++constructor++`` will generate an error.


Before ECMAScript 2015, using duplicate names will generate an error in JavaScript strict mode code.

This rule will also report on duplicate properties in JSX.


=== Noncompliant code example

[source,javascript]
----
let data = {
  "key": "value",
  "1": "value",
  "key": "value", // Noncompliant - duplicate of "key"
  'key': "value", // Noncompliant - duplicate of "key"
  key: "value", // Noncompliant - duplicate of "key"
  \u006bey: "value", // Noncompliant - duplicate of "key"
  "\u006bey": "value", // Noncompliant - duplicate of "key"
  "\x6bey": "value", // Noncompliant - duplicate of "key"
  1: "value" // Noncompliant - duplicate of "1"
}

function MyComponent(props) {
  return <div prop={props.prop1} prop={props.prop2}> { /* Noncompliant, 'prop' is defined twice */ }
    This is my component
  </div>;
}
----

=== Compliant solution

[source,javascript]
----
let data = {
  "key": "value",
  "1": "value",
  "key2": "value",
  'key3': "value",
  key4: "value",
  \u006bey5: "value",
  "\u006bey6": "value",
  "\x6bey7": "value", 
  1b: "value"
}

function MyComponent(props) {
  return <div prop1={props.prop1} prop2={props.prop2}>
    This is my component
  </div>;
}
----

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

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

=== Message

Duplicate name {0}.

or

No duplicate props allowed.


=== Highlighting

primary: the 2nd occurrence

secondar: the first occurrence


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