eslint/lib/rules/no-self-compare.js

/**
 * @fileoverview Rule to flag comparison where left part is the same as the right
 * part.
 * @author Ilya Volodin
 */

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

module.exports = function(context) {
    "use strict";

    return {

        "BinaryExpression": function(node) {
            var operators = ["===", "==", "!==","!=", ">", "<", ">=", "<="];
            if (operators.indexOf(node.operator) > -1 &&
                (node.left.type === "Identifier" && node.right.type === "Identifier" && node.left.name === node.right.name ||
                node.left.type === "Literal" && node.right.type === "Literal" && node.left.value === node.right.value)) {
                context.report(node, "Comparing to itself is potentially pointless.");
            }
        }
    };

};