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Message
TypeError: variable "x" redeclares argument (Firefox)
Error type
TypeError warning in strict mode only.
What went wrong?
The same variable name occurs as a function parameter and is then redeclared using a var assignment in a function body again. This might be a naming conflict and thus JavaScript warns about it.
This error occurs as a warning in strict mode code only. In non-strict code, the redeclaration is silently ignored.
Examples
Invalid cases
In this case, the variable "arg" redeclares the argument.
'use strict';
function f(arg) {
var arg = 'foo';
}
Valid cases
To fix this warning, the var statement can just be omitted, because the variable exists already. In other cases, you might to rename either the function parameter or the variable name.
'use strict';
function f(arg) {
arg = 'foo';
}