eslint-plugin-google-camelcase/lib/rules/google-camelcase.js

enforce camelcase names but allow opt_ prefix

/**
 * @fileoverview Rule to flag non-camelcased identifiers except for the "opt_" prefix
 * @author Gregg Tavares (but it's just a modified version of camelcase by Nicholas C. Zakas)
 */

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

module.exports = function(context) {

    "use strict";

    //--------------------------------------------------------------------------
    // Helpers
    //--------------------------------------------------------------------------

    /**
     * Checks if a string contains an underscore and isn't all upper-case
     * @param {String} name The string to check.
     * @returns {boolean} if the string is underscored
     * @private
     */
    function isUnderscored(name) {
        if (name === "var_args") {
          return false;
        }
        if (name.substring(0, 4) === "opt_") {
            name = name.substring(4);
        }
        // if there's an underscore, it might be A_CONSTANT, which is okay
        return name.indexOf("_") > -1 && name !== name.toUpperCase();
    }

    /**
     * Reports an AST node as a rule violation.
     * @param {ASTNode} node The node to report.
     * @returns {void}
     * @private
     */
    function report(node) {
        context.report(node, "Identifier '{{name}}' is not in camel case.", { name: node.name });
    }

    return {

        "Identifier": function(node) {

            // Leading and trailing underscores are commonly used to flag private/protected identifiers, strip them
            var name = node.name.replace(/^_+|_+$/g, ""),
                effectiveParent = (node.parent.type === "MemberExpression") ? node.parent.parent : node.parent;

            // MemberExpressions get special rules
            if (node.parent.type === "MemberExpression") {

                // Always report underscored object names
                if (node.parent.object.type === "Identifier" &&
                        node.parent.object.name === node.name &&
                        isUnderscored(name)) {
                    report(node);

                // Report AssignmentExpressions only if they are the left side of the assignment
                } else if (effectiveParent.type === "AssignmentExpression" &&
                        isUnderscored(name) &&
                        (effectiveParent.right.type !== "MemberExpression" ||
                        effectiveParent.left.type === "MemberExpression" &&
                        effectiveParent.left.property.name === node.name)) {
                    report(node);
                }

            // Report anything that is underscored that isn't a CallExpression
            } else if (isUnderscored(name) && effectiveParent.type !== "CallExpression") {
                report(node);
            }
        }
    };

};