Assertions in JavaScript

Question

Extensively reading about various assertion frameworks in JavaScript. Is there any kind of de-facto/most common "standard" library/framework? When selecting one - which points are most worth noticing?

The (only) requirement I can think about is close-to-zero performance overhead when in production mode.

Answer 1

Two possible solutions:

Have your build release script remove the Assert lines.

or

Have your build script override the Assert function so it is just an empty function. Downside to this is if you assert call has logic in it [aka assert( x > 100 , "foo" )] than that logic [x > 100] is still going to be run.

Answer 2

Here is what I use:

When I'm working on the code I have initDevMode(); at the top of the file I'm working with, and when I'm ready to release to production, I just remove that line and all the asserts just go to an empty function.

/**
 * Log a message to console:
 *  either use jquery's console.error
 *  or a thrown exception.
 *  
 *  call initDevMode(); before use to activate
 *  use with:
 *      assert(<condition>, "message");
 *      eg: assert(1 != 1, "uh oh!");
 *  
 *  Log errors with:
 *       errorLog(message);
 *       eg: errorLog(xhr.status);
 */
assert = function(test, msg) { }
errorLog =function(msg) { }

initDevMode = function() {
    assert = function(test, msg) {
        msg = msg || "(no error message)";
        if(!test) {
            try {
                    throw Error();
                } catch(e) {
                    var foo = e;
                    var lines = e.stack.split('\n');
                    for(i in lines) {
                        if(i > 2) {
                        errorLog(msg + lines[i]);
                    }
                }
            }
        }
        throw("Assertion failed with: " + msg);
    };
    errorLog = function(msg) {
        if(typeof console.error == 'function') { 
            console.error(msg);
        } else {
            function errorLog(msg) {
                console.log("foo");
                setTimeout(function() {
                    throw new Error(msg);
                }, 0);
            }
        }
    };
}