CodeQL documentation

Useless assignment to local variable

ID: js/useless-assignment-to-local
Kind: problem
Security severity: 
Severity: warning
Precision: very-high
   - maintainability
   - external/cwe/cwe-563
Query suites:
   - javascript-security-and-quality.qls

Click to see the query in the CodeQL repository

A value is assigned to a variable or property, but either that location is never read later on, or its value is always overwritten before being read. This means that the original assignment has no effect, and could indicate a logic error or incomplete code.


Ensure that you check the control and data flow in the method carefully. If a value is really not needed, consider omitting the assignment. Be careful, though: if the right-hand side has a side-effect (like performing a method call), it is important to keep this to preserve the overall behavior.


In the following example, the return value of the call to send on line 2 is assigned to the local variable result, but then never used.

function f(x) {
	var result = send(x);
	return getResponse();

Assuming that send returns a status code indicating whether the operation succeeded or not, the value of result should be checked, perhaps like this:

function f(x) {
	var result = send(x);
	// check for error
	if (result === -1)
		throw new Error("send failed");
	return getResponse();


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