variable has data or not js code example
Example 1: javascript check if boolean is undefined
if (typeof myFlag !== "undefined") {
// comes here whether myFlag is true or false but not defined
}
Example 2: javascript check if undefined or null
// simple check do the job
if (myVar) {
// comes here either myVar is not null,
// or myVar is not undefined,
// or myVar is not '' (empty string).
}