Rule to disallow a duplicate case label (no-duplicate-case)

A switch statements with duplicate case labels is normally an indication of a programmer error.

In the following example the 3rd case label uses again the literal 1 that has already been used in the first case label. Most likely the case block was copied from above and it was forgotten to change the literal.

var a = 1;

switch (a) {
    case 1:
        break;
    case 2:
        break;
    case 1:         // duplicate literal 1
        break;
    default:
        break;
}

Rule Details

This inspection reports any duplicated case labels on JavaScript switch statements.

The following patterns are considered warnings:

var a = 1,
    one = 1;

switch (a) {
    case 1:
        break;
    case 1:
        break;
    case 2:
        break;
    default:
        break;
}

switch (a) {
    case "1":
        break;
    case "1":
        break;
    case "2":
        break;
    default:
        break;
}

switch (a) {
    case one:
        break;
    case one:
        break;
    case 2:
        break;
    default:
        break;
}

The following patterns are not considered warnings:

var a = 1;

switch (a) {
    case 1:
        break;
    case 2:
        break;
    default:
        break;
}

Version

This rule was introduced in ESLint 0.17.0.

Resources