var_exists()
Check whether a variable is declared or not
var_exists(var_name)
var_name
(variable) — Variable name
boolean
— Returns true
if variable is declared, and returns false
if otherwise
var a, b
c = 10
var_exists(a) ' Returns true
var_exists(b) ' Returns true
var_exists(c) ' Returns true
var_exists(d) ' Returns false