noConstantBinaryExpressions

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JavaScript (and super languages)

Summary

Rule available since: v2.0.0
Diagnostic Category: lint/suspicious/noConstantBinaryExpressions
This rule doesn’t have a fix.
The default severity of this rule is information.
Sources:
- Same as no-constant-binary-expression

How to configure

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{
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  "linter": {
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    "rules": {
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      "suspicious": {
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        "noConstantBinaryExpressions": "error"
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      }
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    }
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  }
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}

Description

Disallow expressions where the operation doesn’t affect the value

Comparisons which will always evaluate to true or false and logical expressions (||, &&, ??) which either always short-circuit or never short-circuit are both likely indications of programmer error.

Examples

Invalid

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const value1 = +x == null;

code-block.js:1:16 lint/suspicious/noConstantBinaryExpressions ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ This binary expression leads to a constant result.
  
  > 1 │ const value1 = +x == null;
      │                ^^^^^^^^^^
    2 │

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const value2 = condition ? x : {} || DEFAULT;

code-block.js:1:32 lint/suspicious/noConstantBinaryExpressions ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ This logical expression can be simplified.
  
  > 1 │ const value2 = condition ? x : {} || DEFAULT;
      │                                ^^^^^^^^^^^^^
    2 │ 
  
  ℹ This operand always evaluates to the same truthiness.
  
  > 1 │ const value2 = condition ? x : {} || DEFAULT;
      │                                ^^
    2 │

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const value3 = !foo == null;

code-block.js:1:16 lint/suspicious/noConstantBinaryExpressions ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ This binary expression leads to a constant result.
  
  > 1 │ const value3 = !foo == null;
      │                ^^^^^^^^^^^^
    2 │

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const value4 = new Boolean(foo) === true;

code-block.js:1:16 lint/suspicious/noConstantBinaryExpressions ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ This binary expression leads to a constant result.
  
  > 1 │ const value4 = new Boolean(foo) === true;
      │                ^^^^^^^^^^^^^^^^^^^^^^^^^
    2 │

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const objIsEmpty = someObj === {};

code-block.js:1:20 lint/suspicious/noConstantBinaryExpressions ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ Unexpected comparison to newly constructed object.
  
  > 1 │ const objIsEmpty = someObj === {};
      │                    ^^^^^^^^^^^^^^
    2 │ 
  
  ℹ This expression always constructs a new object.
  
  > 1 │ const objIsEmpty = someObj === {};
      │                                ^^
    2 │

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const arrIsEmpty = someArr === [];

code-block.js:1:20 lint/suspicious/noConstantBinaryExpressions ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ Unexpected comparison to newly constructed object.
  
  > 1 │ const arrIsEmpty = someArr === [];
      │                    ^^^^^^^^^^^^^^
    2 │ 
  
  ℹ This expression always constructs a new object.
  
  > 1 │ const arrIsEmpty = someArr === [];
      │                                ^^
    2 │

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const shortCircuit1 = condition1 && false && condition2;

code-block.js:1:23 lint/suspicious/noConstantBinaryExpressions ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ This logical expression can be simplified.
  
  > 1 │ const shortCircuit1 = condition1 && false && condition2;
      │                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    2 │ 
  
  ℹ This operand always evaluates to the same truthiness.
  
  > 1 │ const shortCircuit1 = condition1 && false && condition2;
      │                       ^^^^^^^^^^^^^^^^^^^
    2 │

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const shortCircuit2 = condition1 || true || condition2;

code-block.js:1:23 lint/suspicious/noConstantBinaryExpressions ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ This logical expression can be simplified.
  
  > 1 │ const shortCircuit2 = condition1 || true || condition2;
      │                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    2 │ 
  
  ℹ This operand always evaluates to the same truthiness.
  
  > 1 │ const shortCircuit2 = condition1 || true || condition2;
      │                       ^^^^^^^^^^^^^^^^^^
    2 │

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const shortCircuit3 = condition1 ?? "non-nullish" ?? condition2;

code-block.js:1:23 lint/suspicious/noConstantBinaryExpressions ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ℹ This logical expression can be simplified.
  
  > 1 │ const shortCircuit3 = condition1 ?? “non-nullish” ?? condition2;
      │                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    2 │ 
  
  ℹ This operand always evaluates to the same nullishness.
  
  > 1 │ const shortCircuit3 = condition1 ?? “non-nullish” ?? condition2;
      │                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^
    2 │

Valid

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const value1 = x == null;

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const value2 = (condition ? x : {}) || DEFAULT;

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const value3 = !(foo == null);

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const value4 = Boolean(foo) === true;

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const objIsEmpty = Object.keys(someObj).length === 0;

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const arrIsEmpty = someArr.length === 0;