node/tools/eslint/lib/rules/no-extra-semi.js

/**
 * @fileoverview Rule to flag use of unnecessary semicolons
 * @author Nicholas C. Zakas
 */

"use strict";

//------------------------------------------------------------------------------
// Rule Definition
//------------------------------------------------------------------------------

module.exports = {
    meta: {
        docs: {
            description: "disallow unnecessary semicolons",
            category: "Possible Errors",
            recommended: true
        },

        fixable: "code",
        schema: []
    },

    create: function(context) {

        /**
         * Reports an unnecessary semicolon error.
         * @param {Node|Token} nodeOrToken - A node or a token to be reported.
         * @returns {void}
         */
        function report(nodeOrToken) {
            context.report({
                node: nodeOrToken,
                message: "Unnecessary semicolon.",
                fix: function(fixer) {
                    return fixer.remove(nodeOrToken);
                }
            });
        }

        /**
         * Checks for a part of a class body.
         * This checks tokens from a specified token to a next MethodDefinition or the end of class body.
         *
         * @param {Token} firstToken - The first token to check.
         * @returns {void}
         */
        function checkForPartOfClassBody(firstToken) {
            for (var token = firstToken;
                token.type === "Punctuator" && token.value !== "}";
                token = context.getTokenAfter(token)
            ) {
                if (token.value === ";") {
                    report(token);
                }
            }
        }

        return {

            /**
             * Reports this empty statement, except if the parent node is a loop.
             * @param {Node} node - A EmptyStatement node to be reported.
             * @returns {void}
             */
            EmptyStatement: function(node) {
                var parent = node.parent,
                    allowedParentTypes = ["ForStatement", "ForInStatement", "ForOfStatement", "WhileStatement", "DoWhileStatement"];

                if (allowedParentTypes.indexOf(parent.type) === -1) {
                    report(node);
                }
            },

            /**
             * Checks tokens from the head of this class body to the first MethodDefinition or the end of this class body.
             * @param {Node} node - A ClassBody node to check.
             * @returns {void}
             */
            ClassBody: function(node) {
                checkForPartOfClassBody(context.getFirstToken(node, 1)); // 0 is `{`.
            },

            /**
             * Checks tokens from this MethodDefinition to the next MethodDefinition or the end of this class body.
             * @param {Node} node - A MethodDefinition node of the start point.
             * @returns {void}
             */
            MethodDefinition: function(node) {
                checkForPartOfClassBody(context.getTokenAfter(node));
            }
        };

    }
};