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noUnsafeOptionalChaining

Diagnostic Category: lint/correctness/noUnsafeOptionalChaining

Since: v1.0.0

Sources:

Disallow the use of optional chaining in contexts where the undefined value is not allowed.

The optional chaining (?.) expression can short-circuit with a return value of undefined. Therefore, treating an evaluated optional chaining expression as a function, object, number, etc., can cause TypeError or unexpected results. Also, parentheses limit the scope of short-circuiting in chains.

Examples

Section titled Examples

Invalid

Section titled Invalid
1 in obj?.foo;
code-block.js:1:9 lint/correctness/noUnsafeOptionalChaining ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ Unsafe usage of optional chaining.
  
  > 1 │ 1 in obj?.foo;
      │         ^^
    2 │ 
  
  ℹ If it short-circuits with ‘undefined’ the evaluation will throw TypeError here:
  
  > 1 │ 1 in obj?.foo;
      │ ^^^^^^^^^^^^^
    2 │ 
  
with (obj?.foo);
code-block.cjs:1:10 lint/correctness/noUnsafeOptionalChaining ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ Unsafe usage of optional chaining.
  
  > 1 │ with (obj?.foo);
      │          ^^
    2 │ 
  
  ℹ If it short-circuits with ‘undefined’ the evaluation will throw TypeError here:
  
  > 1 │ with (obj?.foo);
      │ ^^^^^^^^^^^^^^^^
    2 │ 
  
for (bar of obj?.foo);
code-block.js:1:16 lint/correctness/noUnsafeOptionalChaining ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ Unsafe usage of optional chaining.
  
  > 1 │ for (bar of obj?.foo);
      │                ^^
    2 │ 
  
  ℹ If it short-circuits with ‘undefined’ the evaluation will throw TypeError here:
  
  > 1 │ for (bar of obj?.foo);
      │ ^^^^^^^^^^^^^^^^^^^^^^
    2 │ 
  
bar instanceof obj?.foo;
code-block.js:1:19 lint/correctness/noUnsafeOptionalChaining ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ Unsafe usage of optional chaining.
  
  > 1 │ bar instanceof obj?.foo;
      │                   ^^
    2 │ 
  
  ℹ If it short-circuits with ‘undefined’ the evaluation will throw TypeError here:
  
  > 1 │ bar instanceof obj?.foo;
      │ ^^^^^^^^^^^^^^^^^^^^^^^
    2 │ 
  
const { bar } = obj?.foo;
code-block.js:1:20 lint/correctness/noUnsafeOptionalChaining ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ Unsafe usage of optional chaining.
  
  > 1 │ const { bar } = obj?.foo;
      │                    ^^
    2 │ 
  
  ℹ If it short-circuits with ‘undefined’ the evaluation will throw TypeError here:
  
  > 1 │ const { bar } = obj?.foo;
      │       ^^^^^^^^^^^^^^^^^^
    2 │ 
  
(obj?.foo)();
code-block.js:1:5 lint/correctness/noUnsafeOptionalChaining ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ Unsafe usage of optional chaining.
  
  > 1 │ (obj?.foo)();
      │     ^^
    2 │ 
  
  ℹ If it short-circuits with ‘undefined’ the evaluation will throw TypeError here:
  
  > 1 │ (obj?.foo)();
      │           ^^
    2 │ 
  
(baz?.bar).foo;
code-block.js:1:5 lint/correctness/noUnsafeOptionalChaining ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ Unsafe usage of optional chaining.
  
  > 1 │ (baz?.bar).foo;
      │     ^^
    2 │ 
  
  ℹ If it short-circuits with ‘undefined’ the evaluation will throw TypeError here:
  
  > 1 │ (baz?.bar).foo;
      │            ^^^
    2 │

Valid

Section titled Valid
(obj?.foo)?.();
obj?.foo();
(obj?.foo ?? bar)();
obj?.foo.bar;
obj.foo?.bar;
foo?.()?.bar;
Section titled Related links