16f6c0aecf
Inline adoc files when they are included exactly once. Also fix language tags because this inlining gives us better information on what language the code is written in.
73 lines
1.9 KiB
Plaintext
73 lines
1.9 KiB
Plaintext
== Why is this an issue?
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In TypeScript there are several ways to declare a property with ``++undefined++`` value: adding ``++| undefined++`` in the property type or using optional property syntax (``++?++`` after its name). Use ``++| undefined++`` syntax when you want to be explicit that an object has that property, in that case TypeScript compiler will not allow omitting it:
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----
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interface Person {
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name: string;
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address: string | undefined;
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}
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let John = { name: "John" }; // will not compile
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let John = { name: "John", address: undefined }; // will compile, we want to be explicit when person does not have home
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----
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Use optional property syntax for properties holding some additional information.
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----
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interface Person {
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name: string;
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pet?: string;
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}
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let John = { name: "John" }; // will compile
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let John = { name: "John", pet: undefined }; // will compile, there is no pet like for the object on previous line
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let John = { name: "John", pet: "Benji" }; // will compile
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----
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Using ``++| undefined++`` for optional property is redundant, it can be omitted without change to the actual type. Still if you want to force the property in the object consider using only ``++| undefined++`` without ``++?++``.
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=== Noncompliant code example
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[source,javascript]
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----
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interface Person {
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name: string;
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address? : string | undefined; // Noncompliant, "?" should be removed
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pet?: Animal | undefined; // Noncompliant, "undefined" should be removed
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}
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----
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=== Compliant solution
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[source,javascript]
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----
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interface Person {
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name: string;
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address: string | undefined;
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pet?: Animal;
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}
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----
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ifdef::env-github,rspecator-view[]
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'''
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== Implementation Specification
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(visible only on this page)
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=== Message
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Consider removing 'undefined' type or '?' specifier, one of them is redundant.
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=== Highlighting
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Primary: "?"
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Secondary: "undefined"
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endif::env-github,rspecator-view[]
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