CodeQL documentation

Overwritten property

ID: js/overwritten-property
Kind: problem
Severity: error
Precision: very-high
   - reliability
   - correctness
   - external/cwe/cwe-563
Query suites:
   - javascript-security-and-quality.qls

Click to see the query in the CodeQL repository

In ECMAScript 2015 and above, as well as ECMAScript 5 non-strict mode, an object literal may define the same property multiple times, with later definitions overwriting earlier ones. In particular, if the last definition assigns a different value from earlier definitions, the earlier value is lost, which is most likely unintentional and should be avoided.


Rename the properties to have different names.


In the following example, the object literal assigned to point has two definitions of property x. The object’s use in function dist suggests that the second definition should define a property y instead, and should be renamed.

function dist(p) {
	return Math.sqrt(p.x*p.x+p.y*p.y);

var point = {
	x: 3,
	x: 4


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

  • Ecma International, ECMAScript Language Definition, 6th Edition, Annex E. ECMA, 2015.

  • Common Weakness Enumeration: CWE-563.