How do I implement assertions in JavaScript?

Question

I'd like to use assertions to check for invalid parameters in my private methods (and others that should only be called internally). I'd prefer:

A failed assertion terminates the program, or at least stops my automated tests. console.assert() doesn't appear to do this.
Assertions can be stripped out during production deployment (I'm using Grunt).
A very minimal solution (shouldn't need a library to do this).

EDIT: I'm not trying to test anything here. If my motivation for doing this is unclear, check out CC2 or Clean Code or the Wiki page: https://en.wikipedia.org/wiki/Assertion_(software_development)

1. Why are you testing private methods? 2. Why would you put tests inside actual code? 3. Why not use a testing library? Feels like you're solving the wrong problem here. I bet your real problem is how to test your code properly given some situation you haven't mentioned. — Joseph
– Joseph, Commented Sep 5, 2015 at 4:13
this might be relevant to your concern philipwalton.com/articles/… — Daniel Lizik
– Daniel Lizik, Commented Sep 5, 2015 at 4:26
@JosephtheDreamer Assertions are not just for tests. They serve a complementary role to practices such as exception handling and logging, and are promoted in many programming books such as CC2. — ryan-cook
– ryan-cook, Commented Sep 5, 2015 at 6:13
@Daniel_L Thanks Daniel, but I'm not trying to test these methods. I'm looking to use assertions as "executable documentation" to catch developer mistakes within my code base. I have unit tests in place separately. — ryan-cook
– ryan-cook, Commented Sep 5, 2015 at 6:16

rich remer · Accepted Answer · 2017-11-29 11:10:45Z

1

Something like?

const assert = env === "production"
    ? () => {}
    : (test, msg) =>  {
        if (!test) throw new Error(`assertion failed: ${msg}`);
      };

// ...

function foo(param) {
    assert(typeof param === "number", "param is a Number");
}

edited Nov 29, 2017 at 11:10

answered Sep 5, 2015 at 6:28

rich remer

3,6162 gold badges37 silver badges49 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

ryan-cook Over a year ago

Nice, this meets all of my criteria! I'll accept, but bonus points if anyone can suggest a way to also drop the call statements during minification.

Collectives™ on Stack Overflow

How do I implement assertions in JavaScript?

1 Answer 1

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related