The expected type of the value when it is defined.
The value to check
true if the value is defined (not null and not undefined), narrowing the type to Exclude<T, 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 is not strictly
undefined(and notnull). A string value of"undefined"is considered to be defined. When this returnstrue, TypeScript narrows the type toExclude<T, undefined>, removingundefinedfrom the type.