69 lines
2.6 KiB
Plaintext
69 lines
2.6 KiB
Plaintext
== Why is this an issue?
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In JavaScript, `null` and `undefined` are primitive values that do not have properties or methods. When accessing a property on a `null` or `undefined` value, JavaScript tries to access the property of an object that does not exist, which results in a `TypeError`.
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This can cause the program to crash or behave unexpectedly, which can be difficult to debug.
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[source,javascript,diff-id=1,diff-type=noncompliant]
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----
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let foo = null;
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console.log(foo.bar); // Noncompliant: TypeError will be thrown
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----
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Use the logical AND operator (`&&`) to check if a variable is truthy before attempting to access its properties. The expression will short-circuit and return the falsy value instead of attempting to access its properties.
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[source,javascript,diff-id=1,diff-type=compliant]
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----
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let foo = null;
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console.log(foo && foo.bar);
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----
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Alternatively, use the optional chaining operator (`?.`) to check if the variable is `null` or `undefined` before attempting to access its property. This operator is more readable and concise, especially when dealing with nested properties.
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[source,javascript,diff-id=1,diff-type=compliant]
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----
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let foo = null;
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console.log(foo?.bar);
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----
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== Resources
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=== Documentation
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* https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/undefined[MDN - `undefined`]
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* https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/null[MDN - `null`]
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* https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypeError[MDN - `TypeError`]
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* https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Errors/No_properties[MDN - TypeError: "x" has no properties]
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* https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Optional_chaining[MDN - Optional chaining (``++?.++``)]
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* https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Logical_AND[MDN - Logical AND (``++&&++``)]
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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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include::../message.adoc[]
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include::../highlighting.adoc[]
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'''
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== Comments And Links
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(visible only on this page)
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=== on 15 Mar 2016, 09:45:14 Pierre-Yves Nicolas wrote:
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Useful links:
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* \https://javascriptweblog.wordpress.com/2010/08/16/understanding-undefined-and-preventing-referenceerrors/
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* \https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/undefined
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We could make this rule also cover invalid function calls, e.g.:
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----
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var x = 42;
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x(); // Noncompliant: TypeError will be thrown
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----
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However, there may be some overlap with RSPEC-2999.
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include::../comments-and-links.adoc[]
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endif::env-github,rspecator-view[]
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