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Check if variable is exists in JavaScript

August 29, 2012October 3, 2011 by mkyong

In some cases, your JavaScript may need to depend on a particular variable to “define” or “exists”, in order to process on the next step. Note I don’t recommend to do so, as JavaScript shouldn’t involve any business logic, it should be purely basic validation or UI enhancement, but, many still like to code complex …

Check if variable is a number in JavaScript

August 29, 2012October 2, 2011 by mkyong

In JavaScript, there are two ways to check if a variable is a number : isNaN() – Stands for “is Not a Number”, if variable is not a number, it return true, else return false. typeof – If variable is a number, it will returns a string named “number”. Note Normally, people use isNaN() to …