AI solution for JavaScript Quiz on BFE.dev
134. Object.groupBy

The code provided creates an array of objects called items, where each object has a property id. It then tries to call a function Object.groupBy() which does not exist in Javascript by default. As a result, an error will be thrown when attempting to call this function in the code.

Assuming the Object.groupBy() function is a custom function defined elsewhere in the code (not provided in this snippet), the output of items.toString() will be "[object Object],[object Object]". This is because items is an array with two objects, and when you call toString() on an array, it will concatenate the result of calling toString() on each element in the array.

Similarly, the output of groups.toString() will depend on the implementation of the Object.groupBy() function. Assuming this function groups the items based on their id property and returns an object with keys as the id values and values as arrays of objects with that id, the output could be something like "[object Object],[object Object]" as well (depending on the actual output format of the function).

In summary, the code will throw an error due to the undefined Object.groupBy() function, and the toString() method on the items and groups arrays will return concatenated strings of the objects in the respective arrays.