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
var foo = bar ? bar : 1;
// Good
var foo = bar || 1;
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;
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;
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
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;
You can turn this rule off if you are not concerned with unnecessary complexity in conditional expressions.