jQuery assertion support / defensive programming?

Question

Is there any built in support in jQuery for basic assertion checking, primarily of things like \'expected number of returned elements\'.

For instance I may have a simple

Answer 1

It doesn't look like there is anything built-in. But writing an extension isn't too hard:

$.fn.assertSize = function(size) { 
  if (this.length != size) { 
    alert("Expected " + size + " elements, but got " + this.length + ".");
    // or whatever, maybe use console.log to be more unobtrusive
  }
  return this;
};

Usage is exactly as you propose in your question.

$("#btnSignup").assertSize(1).click(function() {
  return validateForm();
);

Note that in its current form the function returns successfully even if the assertion fails. Anything you have chained will still be executed. Use return false; instead of return this; to stop further execution of the chain.