How to write jQuery code before loading it?

jQuery and various other JS source files are regular part of website built nowadays. But this is always suggested to load JS files at the end of the document. In that case, how you are going to write JS code that requires jQuery to be loaded?

In one of my Web Development tutorial called 10 tips to speed up your website, I also suggested that you should load your JS files at the end of the document.

5. Put JavaScript at bottom:
This is also good practice in site optimization that you load your JS files just before your footer. This will let the browser draw the page without being blocked by JS files loading.

But the problem is, if you load jQuery at the end of the document and try to write jQuery code before that, you will get errors like $ is not defined. So how to write jQuery code before loading jQuery then!

Broadly discuss the measurements of price elasticity of demand.

Measurement of Price Elasticity of Demand: 

There are 5 different measurements of Price Elasticity of Demand. They are as follows:
  1. Perfectly Inelastic Demand (Elasticity = 0)
  2. Perfectly Elastic Demand (Elasticity = Infinity)
  3. Unit Elasticity of Demand (Elasticity = 1)
  4. Relatively Inelastic Demand (Elasticity < 1)
  5. Relatively Elastic Demand (Elasticity > 1)

These measurements has been discussed here. In the following discussion 5 symbols has been used which are

10 Tips on CSS: The Right Way

We know how important CSS is in case of developing UI in web projects. But most of the time we don’t take it seriously. When we are asked to create PSD to HTML, we simply start writing our HTML and CSS. We do not examine the complete PSD to find out similarly styled elements, similarly styled elements with very view changes such as with border radius and without border radius, floated at left and floated at right etc. Instead of examining the full PSD to find out this kind of design patterns we start writing CSS from TOP to BOTTOM.

I would say, that is a very bad practice.