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noUselessTernary (since v1.5.0)

Diagnostic Category: lint/complexity/noUselessTernary

Sources:

Disallow ternary operators when simpler alternatives exist.

It’s a common mistake in JavaScript to use a conditional expression to select between two boolean values instead of using the logical NOT (!) or double NOT (!!) to convert the test to a boolean.

Examples

Section titled Examples

Invalid

Section titled Invalid
var a = x ? true : true;
complexity/noUselessTernary.js:1:9 lint/complexity/noUselessTernary  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━

  ✖ Unnecessary use of boolean literals in conditional expression.
  
  > 1 │ var a = x ? true : true;
      │         ^^^^^^^^^^^^^^^
    2 │ 
  
  ℹ Simplify your code by directly assigning the result without using a ternary operator.
  
  ℹ If your goal is negation, you may use the logical NOT (!) or double NOT (!!) operator for clearer and concise code.
     Check for more details about NOT operator.
  
  ℹ Unsafe fix: Remove the conditional expression with
  
    1 │ var·a·=·x·?·true·:·true;
      │         -----------     

var a = foo === 1 ? false : true;
complexity/noUselessTernary.js:1:9 lint/complexity/noUselessTernary  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━

  ✖ Unnecessary use of boolean literals in conditional expression.
  
  > 1 │ var a = foo === 1 ? false : true;
      │         ^^^^^^^^^^^^^^^^^^^^^^^^
    2 │ 
  
  ℹ Simplify your code by directly assigning the result without using a ternary operator.
  
  ℹ If your goal is negation, you may use the logical NOT (!) or double NOT (!!) operator for clearer and concise code.
     Check for more details about NOT operator.
  
  ℹ Unsafe fix: Remove the conditional expression with
  
    1   │ - var·a·=·foo·===·1·?·false·:·true;
      1 │ + var·a·=·foo·!==1;
    2 2 │   
  

var a = foo + 1 ? false : true;
complexity/noUselessTernary.js:1:9 lint/complexity/noUselessTernary  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━

  ✖ Unnecessary use of boolean literals in conditional expression.
  
  > 1 │ var a = foo + 1 ? false : true;
      │         ^^^^^^^^^^^^^^^^^^^^^^
    2 │ 
  
  ℹ Simplify your code by directly assigning the result without using a ternary operator.
  
  ℹ If your goal is negation, you may use the logical NOT (!) or double NOT (!!) operator for clearer and concise code.
     Check for more details about NOT operator.
  
  ℹ Unsafe fix: Remove the conditional expression with
  
    1   │ - var·a·=·foo·+·1·?·false·:·true;
      1 │ + var·a·=·!(foo·+·1·);
    2 2 │   
  

var a = foo + 1 ? true : false;
complexity/noUselessTernary.js:1:9 lint/complexity/noUselessTernary  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━

  ✖ Unnecessary use of boolean literals in conditional expression.
  
  > 1 │ var a = foo + 1 ? true : false;
      │         ^^^^^^^^^^^^^^^^^^^^^^
    2 │ 
  
  ℹ Simplify your code by directly assigning the result without using a ternary operator.
  
  ℹ If your goal is negation, you may use the logical NOT (!) or double NOT (!!) operator for clearer and concise code.
     Check for more details about NOT operator.
  
  ℹ Unsafe fix: Remove the conditional expression with
  
    1   │ - var·a·=·foo·+·1·?·true·:·false;
      1 │ + var·a·=·!!(foo·+·1·);
    2 2 │

Valid

Section titled Valid
var a = x === 2 ? 'Yes' : 'No';
var a = x === 2 ? 'Yes' : false;

Resources

Section titled Resources

Logical NOT: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Logical_NOT

Section titled Related links