ermock

Express middleware to mock requests with JSON and JS files.

Features

• File based mocks using JSON and JS files.
• Flexible configuration with rcload.
• Supports preflight requests using cors.
• Uses express style path matching with path-to-regexp.

Installation

npm i ermock

Usage

const express = require("express");
const ermock = require("ermock");

const app = express();

// Add middleware as early as possible.
app.use(ermock());

// Setup routes etc.

Setup

It uses rcload and thus supports the following:

• ermock property in package.json
• .ermockrc file in JSON format
• .ermockrc.json or .ermockrc.js file
• ermock.config.js file exporting a JS object

Furthemore it also accepts a configuration object when setting up in express, eg.:

app.use(mocker({
    root: "/api",
    dir: "my-mock-reposnses",
    delay: 500,
    table: { ... }
}));

The complete configuration will consist of default values, file based configuration (cosmiconfig) and object based configuration merged in the mentioned order.
This makes it possible to dynamically overwrite properties, e.g. the root prefix upon application load.

Configuration

The configuration object accepts the following properties:

Property	Type	Default value	Description
root	string	""	Path prefix, e.g. "/api"
dir	string	""	Folder name where mock files can be found, e.g. "mocks"
table	string or object	{}	Filename or object with url path as key and filename as key, see below.
delay	number	0	Add delay to reponses in milliseconds.
corsOptions	object	{}	Options object to use with cors.

Table configuration

The table accepts either a filename (relative to application root) or an object with the table configuration.
If you supply a filename it will be loaded automatically, e.g. mocks/table.json or mock-table.json.

The object must:

• have url path as key, starting with forward slash and excluding the root prefix.
• have filename as value, either a .json file or .js file returning a method.

The path matching is done with path-to-regexp using default options.

Example of table configuration:

// mock-table.json
{
    "/myservice/users": "users.json",
    "/myservice/user/:id": "user.js
}

// users.json
{
    "users": [
        1,
        2
    ]
}

// user.js
module.exports = function (props) {
    const { id } = props;

    if (id === 1) {
        return {
            id,
            name: "Arnold S.",
            email: "[email protected]",
            username: "T800",
            permissions: ["ALL"]
        };
    } else {
        return {
            id,
            name: "Connor, Sarah",
            email: "",
            username: "donttrustthemachines",
            permissions: ["RESTRICTED"]
        }
    }

}

When a method is returned from the mock file, it is executed with the match object containing named keys and indexed values from the path matched. See the following example:

// table config
{
    "/service/subscription/:id([^/\\?]+)(\\?.*)?": "mockfile.js"
}

// req url:
//  "/service/subscription/123?userinfo=true"

// mockfile.js
module.exports = function (props) {
    // props = { '0': '?userinfo=true', id: '123' }
}

For detailed configuration of the url path, see the path-to-regexp readme.

License

MIT