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disallow ternary operators when simpler alternatives exist (no-unneeded-ternary)

The --fix option on the command line can automatically fix some of the problems reported by this rule.

It’s a common mistake in JavaScript to use a conditional expression to select between two Boolean values instead of using ! to convert the test to a Boolean. Here are some examples:

// Bad
var isYes = answer === 1 ? true : false;

// Good
var isYes = answer === 1;


// Bad
var isNo = answer === 1 ? false : true;

// Good
var isNo = answer !== 1;

Another common mistake is using a single variable as both the conditional test and the consequent. In such cases, the logical OR can be used to provide the same functionality. Here is an example:

// Bad
foo(bar ? bar : 1);

// Good
foo(bar || 1);

Rule Details

This rule disallow ternary operators when simpler alternatives exist.

Examples of incorrect code for this rule:

/*eslint no-unneeded-ternary: "error"*/

var a = x === 2 ? true : false;

var a = x ? true : false;

var a = f(x ? x : 1);

Examples of correct code for this rule:

/*eslint no-unneeded-ternary: "error"*/

var a = x === 2 ? "Yes" : "No";

var a = x !== false;

var a = x ? "Yes" : "No";

var a = x ? y : x;

var a = x ? x : 1;  // Note that this is only allowed as it on the right hand side of an assignment; this type of ternary is disallowed everywhere else. See defaultAssignment option below for more details.

Options

This rule has an object option:

  • "defaultAssignment": true (default) allows the conditional expression as a default assignment pattern
  • "defaultAssignment": false disallows the conditional expression as a default assignment pattern

defaultAssignment

The defaultAssignment option allows expressions of the form x ? x : expr (where x is any identifier and expr is any expression) as the right hand side of assignments (but nowhere else).

Examples of additional incorrect code for this rule with the { "defaultAssignment": false } option:

/*eslint no-unneeded-ternary: ["error", { "defaultAssignment": false }]*/

var a = x ? x : 1;

When Not To Use It

You can turn this rule off if you are not concerned with unnecessary complexity in conditional expressions.

Version

This rule was introduced in ESLint 0.21.0.

Resources

© JS Foundation and other contributors
Licensed under the MIT License.
https://eslint.org/docs/rules/no-unneeded-ternary