Avoid assignment operators in conditional expressions

Documentos > Datadog Security > Seguridad del código > Static Code Analysis (SAST) > Reglas de SAST > Avoid assignment operators in conditional expressions

This page is not yet available in Spanish. We are working on its translation.
If you have any questions or feedback about our current translation project, feel free to reach out to us!

Metadata

ID: javascript-best-practices/no-cond-assign

Language: JavaScript

Severity: Error

Category: Best Practices

Description

While there might be valid reasons to use an assignment operation in a condition, it is very easy to mistake = with the more usual intended ==. This rule prevents such mistakes, as it is easier to intentionally disable the rule than identify the error.

Non-Compliant Code Examples

var x; if (x = 0) { var b = 1; }
var x; while (x = 0) { var b = 1; }
var x = 0, y; do { y = x; } while (x = x + 1);
var x; for(; x+=1 ;){};
var x; if ((x) = (0));
if (someNode || (someNode = parentNode)) { }
if (someNode || (someNode = parentNode)) { }
while (someNode || (someNode = parentNode)) { }
do { } while (someNode || (someNode = parentNode));
for (; typeof l === 'undefined' ? (l = 0) : l; i++) { }
if (x = 0) { }
while (x = 0) { }
do { } while (x = x + 1);
for(; x = y; ) { }
var x; var b = (x = 0) ? 1 : 0;
var x; var b = x && (y = 0) ? 1 : 0;
(((3496.29)).bkufyydt = 2e308) ? foo : bar;


if ((someNode = someNode.parentNode) !== null) { }
if ((someNode = someNode.parentNode) !== null) { }
if (someNode || (someNode = parentNode)) { }
while (someNode || (someNode = parentNode)) { }
do { } while (someNode || (someNode = parentNode));
for (;someNode || (someNode = parentNode););

Compliant Code Examples

var x = 0; if (x == 0) { var b = 1; }
var x = 0; if (x == 0) { var b = 1; }
var x = 5; while (x < 5) { x = x + 1; }
if ((a = b));
while ((a = b));
do {} while ((a = b));
for (;(a = b););
for (;;) {}
if ((function(node) { return node = parentNode; })(someNode)) { }
if ((function(node) { return node = parentNode; })(someNode)) { }
if ((node => node = parentNode)(someNode)) { }
if ((node => node = parentNode)(someNode)) { }
if (function(node) { return node = parentNode; }) { }
if (function(node) { return node = parentNode; }) { }
x = 0;
var x; var b = (x === 0) ? 1 : 0;
switch (foo) { case a = b: bar(); }
switch (foo) { case a = b: bar(); }
switch (foo) { case baz + (a = b): bar(); }