no-unneeded-ternary.md

规则名	规则类型	关联规则
no-unneeded-ternary	suggestion	no-ternary no-nested-ternary

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:

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

// 正确
var isYes = answer === 1;

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

// 正确
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:

// 错误
foo(bar ? bar : 1);

// 正确
foo(bar || 1);

规则详解

This rule disallow ternary operators when simpler alternatives exist.

此规则的 错误 代码实例：

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

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

var a = x ? true : false;

此规则的 正确 代码实例：

::: correct

/*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;

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

配置项

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:

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

var 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).

禁用建议

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