How to test JavaScript without a framework

It depends whether you are trying to test Node.js code or front end code. In both cases you have to "expose" the function under test to your test framework.

Node.js

// main.js

const obj = {};

obj.sum = (a, b) => {
  return a+b;
};

module.exports = obj; // Export 'obj' so that it is visible from your test runner

// test.js
const main = require('main.js');
const assert = require('assert');

const it = (desc, fn) => {
  try {
    fn();
    console.log('\x1b[32m%s\x1b[0m', `\u2714 ${desc}`);
  } catch (error) {
    console.log('\n');
    console.log('\x1b[31m%s\x1b[0m', `\u2718 ${desc}`);
    console.error(error);
  }
};

it('should return the sum of two numbers', () => {
  assert.strictEqual(main.sum(5, 10), 15);
});

When you run node test.js you should be able to see the test result.

Front End

// app.js
self.myapp = myapp; // All the methods in myapp will be exposed globally

myapp.sum = function(a, b) {
  return a + b;
}

// test.js
function it(desc, fn) {
  try {
    fn();
    console.log('\x1b[32m%s\x1b[0m', '\u2714 ' + desc);
  } catch (error) {
    console.log('\n');
    console.log('\x1b[31m%s\x1b[0m', '\u2718 ' + desc);
    console.error(error);
  }
}

function assert(condition) {
  if (!condition) {
    throw new Error();
  }
}

it('should return a sum of two integers', function(){
  assert(myapp.sum(5, 10) === 15);
});


// test.html - This is your test runner for the front end
<html>
...
<body>
...
<script src="app.js"></script>
<script src="test.js"></script>
</body>
</html>

Open test.html in a browser and open the browser console. You should be able to see the success message.

This way you can write test cases for Node.js and front end JavaScript code without using Mocha or any other framework.

To make your code work, your testMain.js file needs to import your main.js code somehow.

In the main.js file:

function calculate(a, b) {
    return a+b;
}

module.exports.calculate = calculate

in testMain.js file, import the main.js:

var main = require('main.js')

function testCalculate(){
    if(main.calculate(1+1)==2)
       console.log('It Works!');
    else
       console.log('Test failed');
}

Note: I'm aware this isn't necessarily showing good coding style, just aiming to demonstrate what the original issue was with minimal changes to the original snippets

That said, it's not usually worth reinventing the wheel and building your own test framework. Can you clarify the reason why you would like to avoid an existing framework? If you are looking for simplicity, maybe something like jstinytest would do the trick.

If it is a Node.js application you can simply require the other file and import the other function. If the project uses Babel you can use ES6 import to import the function from the other file.

I was also bothered by the same issue for a while. The question is how to test your JavaScript code with out a testing framework since testing frame works bring a lot to the table and most of the time they get into the way.

• The answer is to use assertion libraries without the testing frame work. For example you can just use chai assertion library with out mocha frame work

you can simple install chai with npm install chai
After that you can just use it:

var should = require('chai').should() 

const log = console.log;

//log(should);

//const letters = "abcdef";

const letters = 555;


letters.should.be.a('string');