I do not understand what you mean. But it sounds like you are into functional programming !? Which works fine without type annotations. For example:

const sum = (number, number) => number+number

Where type annotations becomes unnecessary verbose.

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.

You can use an auto-generated intermediate format when running the tests, that check each member object, give test coverage, etc. Eg. a tool that parses the code and inserts a bunch of checks above each member access. So you start with plain JavaScript, and you ship plain JavaScript.