no-duplicate-case
The "extends": "eslint:recommended"
property in a configuration file enables this rule.
Disallows duplicate case
labels.
If a switch
statement has duplicate test expressions in case
clauses, it is likely that a programmer copied a case
clause but forgot to change the test expression.
Rule Details
This rule disallows duplicate test expressions in case
clauses of switch
statements.
Examples of incorrect code for this rule:
/*eslint no-duplicate-case: "error"*/ var a = 1, one = 1; switch (a) { case 1: break; case 2: break; case 1: // duplicate test expression break; default: break; } switch (a) { case one: break; case 2: break; case one: // duplicate test expression break; default: break; } switch (a) { case "1": break; case "2": break; case "1": // duplicate test expression break; default: break; }
Examples of correct code for this rule:
/*eslint no-duplicate-case: "error"*/ var a = 1, one = 1; switch (a) { case 1: break; case 2: break; case 3: break; default: break; } switch (a) { case one: break; case 2: break; case 3: break; default: break; } switch (a) { case "1": break; case "2": break; case "3": break; default: break; }
When Not To Use It
In rare cases where identical test expressions in case
clauses produce different values, which necessarily means that the expressions are causing and relying on side effects, you will have to disable this rule.
switch (a) { case i++: foo(); break; case i++: // eslint-disable-line no-duplicate-case bar(); break; }
Version
This rule was introduced in ESLint 0.17.0.
Resources
© OpenJS Foundation and other contributors
Licensed under the MIT License.
https://eslint.org/docs/rules/no-duplicate-case