noConstantCondition

JavaScript (and super languages)

Summary

• Rule available since: v1.0.0
• Diagnostic Category: lint/correctness/noConstantCondition
• This rule is recommended, which means is enabled by default.
• This rule doesn’t have a fix.
• The default severity of this rule is error.
• Sources:
  • Same as no-constant-condition

How to configure

biome.json

{
  "linter": {
    "rules": {
      "correctness": {
        "noConstantCondition": "error"
      }
    }
  }
}

Description

Disallow constant expressions in conditions

Examples

Invalid

if (false) {
    doSomethingUnfinished();
}

code-block.js:1:5 lint/correctness/noConstantCondition ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ Unexpected constant condition.
  
  > 1 │ if (false) {
      │     ^^^^^
    2 │     doSomethingUnfinished();
    3 │ }
  

if (Boolean(1)) {
    doSomethingAlways();
}

code-block.js:1:5 lint/correctness/noConstantCondition ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ Unexpected constant condition.
  
  > 1 │ if (Boolean(1)) {
      │     ^^^^^^^^^^
    2 │     doSomethingAlways();
    3 │ }
  

if (undefined) {
    doSomethingUnfinished();
}

code-block.js:1:5 lint/correctness/noConstantCondition ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ Unexpected constant condition.
  
  > 1 │ if (undefined) {
      │     ^^^^^^^^^
    2 │     doSomethingUnfinished();
    3 │ }
  

for (;-2;) {
    doSomethingForever();
}

code-block.js:1:7 lint/correctness/noConstantCondition ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ Unexpected constant condition.
  
  > 1 │ for (;-2;) {
      │       ^^
    2 │     doSomethingForever();
    3 │ }
  

while (typeof x) {
    doSomethingForever();
}

code-block.js:1:8 lint/correctness/noConstantCondition ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ Unexpected constant condition.
  
  > 1 │ while (typeof x) {
      │        ^^^^^^^^
    2 │     doSomethingForever();
    3 │ }
  

var result = 0 ? a : b;

code-block.js:1:14 lint/correctness/noConstantCondition ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ Unexpected constant condition.
  
  > 1 │ var result = 0 ? a : b;
      │              ^
    2 │ 
  

Valid

if (x === 0) {
    doSomething();
}

for (;;) {
    doSomethingForever();
}

while (typeof x === "undefined") {
    doSomething();
}

do {
    doSomething();
} while (x);

var result = x !== 0 ? a : b;

// Exception
while (true) {
    if (x) { break; }
    x = f();
}

Related links

• Disable a rule
• Configure the code fix
• Rule options
• Source Code
• Test Cases