CodeQL documentation

Whitespace contradicts operator precedence

ID: js/whitespace-contradicts-precedence
Kind: problem
Severity: warning
Precision: very-high
Tags:
   - maintainability
   - correctness
   - statistical
   - non-attributable
   - external/cwe/cwe-783
Query suites:
   - javascript-security-and-quality.qls

Click to see the query in the CodeQL repository

Nested expressions where the spacing around operators suggests a different grouping than that imposed by the JavaScript operator precedence rules are problematic: they could indicate a bug where the author of the code misunderstood the precedence rules. Even if there is no a bug, the spacing could be confusing to people who read the code.

Recommendation

Make sure that the spacing around operators reflects operator precedence, or use parentheses to clarify grouping.

Example

Consider the following piece of code for allocating an array:

var a = new Array(capacity + capacity>>1);

Here, the spacing around + and >> suggests the grouping capacity + (capacity>>1), that is, the allocated array should be 50% larger than the given capacity.

However, + has higher precedence than >>, so this code allocates an array of size (capacity + capacity) >> 1, which is the same as capacity.

To fix this issue, parentheses should be used like this:

var a = new Array(capacity + (capacity>>1));

References

  • J. Bloch and N. Gafter, Java Puzzlers: Traps, Pitfalls, and Corner Cases, Puzzle 35. Addison-Wesley, 2005.

  • Common Weakness Enumeration: CWE-783.