The value to check
true if arg has a value (is not === undefined)
isDefined(null); // false
isDefined(undefined); // false
isDefined("undefined"); // true
let value = null;
isDefined(value); // false
let value = undefined;
isDefined(value); // false
isDefined(""); // true
isDefined(0); // true
isDefined(new Date()); // true
isDefined(true); // true
isDefined(false); // true
Checks if the passed value is defined, which means it has any value and is not undefined. A string value of "undefined" is considered to be defined.