Answers for "how to check if a variable exists"

javascript check if variable exists

if (typeof myVar !== 'undefined') {
    // myVar is defined
}

how to check if a variable exists in python

#if the variable is local: 
if 'myVar' in locals():
  # myVar exists

#if the variable is global:
if 'myVar' in globals():
  # myVar exists.