True. Consider this example:

    props.removes[cc] !== props.last.margin

TypeScript's strict types will see the error if the those are not the same data type. A TypeScript aware editor will yell at me before I compile the code. Perhaps what I really wanted is:

    props.removes[cc][0] !== props.last.margin

In JavaScript I would have to execute the code. If the code doesn't throw an error then I would have to examine the output to see if the resulting data structure matches what I expect. If not I have to run tests and track down the error. Then once the error is found and resolved I have to write unit tests for this scenario.