Date: 2019jan3 Language: javaScript Keywords: is_defined, isDefined Q. What's the best way to check if a javaScript global variable is defined? A. If you use the variable anywhere but in typeof() you get an error. So that means the solution is to use typeof()

if (typeof(gMyGlobal) !== 'undefined') { console.log('is is defined'); }

Or you can make a function

function isMyGlobalDefined() { return typeof(gMyGlobal) !== 'undefined'; }

Note we use 'undefined' unquotes and not undefined because typeof() returns a string.