JavaScript SyntaxError - Redeclaration of formal parameter "x"
Last Updated :
24 Jul, 2020
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This JavaScript exception redeclaration of formal parameter occurs if a variable name is a function parameter and also declared again inside the function body using a let assignment.
Message:
SyntaxError: Let/Const redeclaration (Edge) SyntaxError: redeclaration of formal parameter "x" (Firefox) SyntaxError: Identifier "x" has already been declared (Chrome)
Error Type:
SyntaxError
Cause of Error: In a function declaration, a variable name in the function parameter and inside the function body, same variable name declared using a let assignment.
Example 1: In this example, the 'let' keyword is used to re-declare the parameter variable, So the error has occurred.
<!DOCTYPE html>
<html>
<head>
<title>Syntax Error</title>
</head>
<body>
<script>
function GFG(var_name) {
let var_name = 'This is GFG';
return var_name;
}
document.write(GFG());
</script>
</body>
</html>
Output(In console):
SyntaxError: Let/Const redeclaration
Example 2: In this example, the 'const' keyword is used to re-declare the parameter variable, So the error has occurred.
<!DOCTYPE html>
<html>
<head>
<title>Syntax Error</title>
</head>
<body>
<script>
function GFG(var_name) {
const var_name = 12345;
return var_name;
}
document.write(GFG());
</script>
</body>
</html>
Output(In console):
SyntaxError: Let/Const redeclaration
