jscs/lib/rules/disallow-trailing-comma.js

/**
 * Disallows an extra comma following the final element of an array or object literal.
 *
 * Type: `Boolean`
 *
 * Value: `true`
 *
 * JSHint: [`es3`](http://jshint.com/docs/options/#es3)
 *
 * #### Example
 *
 * ```js
 * "disallowTrailingComma": true
 * ```
 *
 * ##### Valid
 *
 * ```js
 * var foo = [1, 2, 3];
 * var bar = {a: "a", b: "b"}
 * const [1, 2, 3];
 * const {a: "a", b: "b"}
 * ```
 *
 * ##### Invalid
 *
 * ```js
 * var foo = [1, 2, 3, ];
 * var bar = {a: "a", b: "b", }
 * ```
 */

var assert = require('assert');

module.exports = function() {};

module.exports.prototype = {
    configure: function(options) {
        assert(
            options === true,
            this.getOptionName() + ' option requires a true value or should be removed'
        );
    },

    getOptionName: function() {
        return 'disallowTrailingComma';
    },

    check: function(file, errors) {
        file.iterateNodesByType([
            'ObjectExpression', 'ArrayExpression',
            'ObjectPattern', 'ArrayPattern'
        ], function(node) {
            var closingToken = file.getLastNodeToken(node);
            var comma = closingToken.getPreviousCodeToken();

            if (comma.type === 'Punctuator' && comma.value === ',') {
                errors.add(
                    'Extra comma following the final element of an array or object literal',
                    comma
                );
            }
        });
    },

    _fix: function(file, error) {
        error.element.remove();
    }

};