Debugging with assertions - console.assert

Writes an error message to the console if the assertion is false. Otherwise, if the assertion is true, this does nothing.

console.assert('one' === 1);

Multiple arguments can be provided after the assertion–these can be strings or other objects–that will only be printed if the assertion is false:

console.assert does not throw an AssertionError (except in Node.js), meaning that this method is incompatible with most testing frameworks and that code execution will not break on a failed assertion.