CodeQL documentation

Duplicate parameter names

ID: js/duplicate-parameter-name
Kind: problem
Severity: error
Precision: very-high
   - reliability
   - correctness
Query suites:
   - javascript-security-and-quality.qls

Click to see the query in the CodeQL repository

In non-strict mode, JavaScript allows a function to have several parameters with the same name, where later parameters shadow earlier parameters. This is an error-prone feature which makes code hard to understand and should be avoided.


Rename the parameters to have different names.


In the following example, function f has two parameters named x, the second one presumably being a typo for y. Since no parameter y is declared, the use of y in the body of f refers to a global variable of that name, if it exists.

function f(x, x) {
	return x+y;

Duplicate parameter names are illegal in strict mode.


  • Ecma International, ECMAScript Language Definition, 5.1 Edition, Annex C. ECMA, 2011.