TypeScript Array Object Methods: Returns a new array comprised of this array joined with other array (s) and/or value (s). Returns true if every element in this array satisfies the provided testing function. Creates a new array with all of the elements of this array for which the provided filtering function returns true.. Object.keys. Sometimes it is still useful to just loop through each property on an object in order to do something. I find that I use it for unit testing, but there's other applications, too. Object.keys allows you to enumerate the properties of an object, returning you an array of string which represent the property names. You can then, if. "/>Typescript array of objects with keys