In the for-in loop iterating over an object, what output will be produced from { name: 'Lydia', age: 21 }?

When using a for-in loop to iterate over the properties of an object, the loop generates an iteration for each key in the object. In the provided example, the object consists of two properties: "name" and "age".

During each iteration of the for-in loop, the variable assigned to hold the property name will receive the name of that property. Therefore, as the loop progresses through the object, the first iteration will assign "name" to the variable, and the second will assign "age" as the loop completes.

The output generated is a sequence of the property names as strings, which in this case are "name" and "age". Thus, the result of the for-in loop in this scenario will yield those property names specifically.

This understanding clarifies that the other options do not align with the expected behavior of a for-in loop. The first option incorrectly represents the output format, the third option shows the values of the properties rather than their names, and the last option suggests a format that combines keys and values in arrays, which does not accurately reflect what the for-in loop produces.