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(context) {
        const sourceCode = context.getSourceCode();

        /**
         * 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(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 (let token = firstToken;
                token.type === "Punctuator" && token.value !== "}";
                token = sourceCode.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(node) {
                const parent = node.parent,
                    allowedParentTypes = [
                        "ForStatement",
                        "ForInStatement",
                        "ForOfStatement",
                        "WhileStatement",
                        "DoWhileStatement",
                        "IfStatement",
                        "LabeledStatement",
                        "WithStatement"
                    ];

                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(node) {
                checkForPartOfClassBody(sourceCode.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(node) {
                checkForPartOfClassBody(sourceCode.getTokenAfter(node));
            }
        };

    }
};