The design of JavaScript is not so sophisticated. It's very easy for us to make mistakes if we are not very careful when using JavaScript. For example, to check the existence of JavaScript object.Now we want to check whether a global object myObj exists or not, if it doesn't exist, we declare it. The pseudo code for this is :if(myObj not exist){ declare myObj;}You may think it's very easy to write the code. In fact, it is much more difficult than we may think. Juriy Zaytsev says there are more than 50 ways to check whether a JavaScript object exist or not. Only if you are very clear about the ...