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--
js_formal_parameter_error.js:1:13 parse ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  × Type annotations are a TypeScript only feature. Convert your file to a TypeScript file or remove the syntax.
  
  > 1 │ function a(x: string) {}
      │             ^^^^^^^^
    2 │ function b(x?) {}
    3 │ 
  
  i TypeScript only syntax
  
--
js_formal_parameter_error.js:2:13 parse ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  × optional parameters are a TypeScript only feature. Convert your file to a TypeScript file or remove the syntax.
  
    1 │ function a(x: string) {}
  > 2 │ function b(x?) {}
      │             ^
    3 │ 
  
  i TypeScript only syntax
  
--
function a(x: string) {}
function b(x?) {}