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
const isYes = answer === 1 ? true : false;

// Good
const isYes = answer === 1;

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

// Good
const 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:

::: incorrect

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

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

const b = x ? true : false;

:::

Examples of correct code for this rule:

::: correct

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

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

const b = x !== false;

const c = x ? "Yes" : "No";

const d = x ? y : x;

f(x ? x : 1); // default assignment - would be disallowed if defaultAssignment option set to false. See option details below.

:::

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

When set to true, which it is by default, The defaultAssignment option allows expressions of the form x ? x : expr (where x is any identifier and expr is any expression).

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

::: incorrect

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

const a = x ? x : 1;

f(x ? x : 1);

:::

Note that defaultAssignment: false still allows expressions of the form x ? expr : x (where the identifier is on the right hand side of the ternary).

When Not To Use It

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