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SyntaxError: redeclaration of formal parameter "x"

SyntaxError: redeclaration of formal parameter "x" (Firefox)
SyntaxError: Identifier "x" has already been declared (Chrome)

In this article

SyntaxError

?

, let. JavaScript let.

"arg" :

js
function f(arg) {
  let arg = "foo";
}

// SyntaxError: redeclaration of formal parameter "arg"

"arg" , , . , let . , , .

js
function f(arg) {
  arg = "foo";
}

function f(arg) {
  let bar = "foo";
}

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  1. JavaScript
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    75. SyntaxError: private fields can't be deleted
    76. SyntaxError: property name __proto__ appears more than once in object literal
    77. SyntaxError: raw bracket is not allowed in regular expression with unicode flag
    78. SyntaxError: redeclaration of formal parameter "x"
    79. SyntaxError: reference to undeclared private field or method #x
    80. SyntaxError: rest parameter may not have a default
    81. SyntaxError: return not in function
    82. SyntaxError: setter functions must have one argument
    83. SyntaxError: string literal contains an unescaped line break
    84. SyntaxError: super() is only valid in derived class constructors
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    95. TypeError: "x" is not a constructor
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    103. TypeError: can't assign to property "x" on "y": not an object
    104. TypeError: can't convert BigInt to number
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    106. TypeError: can't define property "x": "obj" is not extensible
    107. TypeError: can't delete non-configurable array element( : )
    108. TypeError: can't redefine non-configurable property "x"
    109. TypeError: can't set prototype of this object
    110. TypeError: can't set prototype: it would cause a prototype chain cycle
    111. TypeError: cannot use 'in' operator to search for 'x' in 'y'( 'in' 'x' 'y')
    112. TypeError: class constructors must be invoked with 'new'
    113. TypeError: cyclic object value
    114. TypeError: derived class constructor returned invalid value x
    115. TypeError: getting private setter-only property
    116. TypeError: Initializing an object twice is an error with private fields/methods
    117. TypeError: invalid 'instanceof' operand 'x'( : '' '')
    118. TypeError: invalid Array.prototype.sort argument (TypeError: Array.prototype.sort argument)
    119. TypeError: invalid assignment to const "x"( const "x")
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    122. TypeError: More arguments needed
    123. TypeError: "x" has no properties
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    128. X.prototype.y called on incompatible type
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