SyntaxError: redeclaration of formal parameter "x"
The JavaScript exception "redeclaration of formal parameter" occurs when the samevariable name occurs as a function parameter and is then redeclared using alet assignment in a function body again.
Message
SyntaxError: Identifier "x" has already been declared (V8-based)SyntaxError: redeclaration of formal parameter "x" (Firefox)SyntaxError: Cannot declare a let variable twice: 'x'. (Safari)
Error type
SyntaxErrorWhat went wrong?
The same variable name occurs as a function parameter and is then redeclared using alet assignment in a function body again. Redeclaring thesame variable within the same function or block scope usinglet is notallowed in JavaScript.
Examples
Redeclared argument
In this case, the variable "arg" redeclares the argument.
function f(arg) { let arg = "foo";}// SyntaxError: redeclaration of formal parameter "arg"If you want to change the value of "arg" in the function body, you can do so, but youdo not need to declare the same variable again. In other words: you can omit thelet keyword. If you want to create a new variable, you need to rename it asconflicts with the function parameter already.
function f(arg) { arg = "foo";}function g(arg) { let bar = "foo";}