eslint/lib/rules/no-undef.js

/**
 * @fileoverview Rule to flag references to undeclared variables.
 * @author Mark Macdonald
 */
"use strict";

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

function isImplicitGlobal(variable) {
    return variable.defs.every(function(def) {
        return def.type === "ImplicitGlobalVariable";
    });
}

/**
 * Gets the declared variable, defined in `scope`, that `ref` refers to.
 * @param {Scope} scope The scope in which to search.
 * @param {Reference} ref The reference to find in the scope.
 * @returns {Variable} The variable, or null if ref refers to an undeclared variable.
 */
function getDeclaredGlobalVariable(scope, ref) {
    var declaredGlobal = null;
    scope.variables.some(function(variable) {
        if (variable.name === ref.identifier.name) {
            // If it's an implicit global, it must have a `writeable` field (indicating it was declared)
            if (!isImplicitGlobal(variable) || {}.hasOwnProperty.call(variable, "writeable")) {
                declaredGlobal = variable;
                return true;
            }
        }
        return false;
    });
    return declaredGlobal;
}

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

module.exports = function(context) {

    return {

        "Program": function(/*node*/) {

            var globalScope = context.getScope();

            globalScope.through.forEach(function(ref) {
                var variable = getDeclaredGlobalVariable(globalScope, ref),
                    name = ref.identifier.name;
                if (!variable) {
                    context.report(ref.identifier, "'{{name}}' is not defined.", { name: name });
                } else if (ref.isWrite() && variable.writeable === false) {
                    context.report(ref.identifier, "'{{name}}' is read only.", { name: name });
                }
            });
        }
    };

};