Scenarios for Re-using Variables within the Same JavaScript Function: Always a No No?

I've just finished writing a script for parsing csv data. Having recently installed JShint, it's been badgering me about the re-use of variables. I've been using JS a fair bit lately, but I come from a python background where it's normal to reuse variables. I'm wondering what issues there are with reusing variables in the following two examples:

Loop with a Switch

The following loop steps through the rows on a csv file, and when it passes a certain value in a row, it switches variable "currentSwitch" from false to true. After currentSwitch is tripped, the loop starts to push stuff to an array.

for (f=0; f < data.length; f++){
        if (data[f][0] === code){
            if (currentSwitch === true){
                dataListByCode.push(data[f]);
            }
        }
        else if ((data[f][0]).slice(0,4) === "UNIN"){
            var currentSwitch = true;
        }
    }

Processing Data with Broken Out Functions

I've got a few functions for processing data that it makes sense to keep separate. In the following code, I process with one function, then I process with another.

var dataListByCode = addDivideData(dataListByCode);
var dataListByCode = addBeforeEntriesArray(dataListByCode, invNumber, matterNumber, client, workType);

Can anyone tell me if this is not in line with best practice? Is there anything that could go wrong with either of these (or scenarios like them)?

You don't need to redeclare currentSwtich

var currentSwitch = true;

In fact it really doesn't make any sense to redeclare this variable in the middle of the loop and in most cases it's almost certainly not what you actually want.

Just initialize/declare it once at the beginning of your loop

var currentSwtich;
// or
var currentSwitch = false;

and drop the var when you set it to true:

currentSwitch = true;

Basically what you are doing is creating a brand new variable with the same name as the old one, and throwing away the old one. This isn't really what you want normally.

There is no analogous concept in python because python doesn't require you to declare variables.

The major problem with reusing variables is that:

a.) in bigger code blocks it can get very confusing, especially if you added/removed code ~20 times, and kept reusing same ~5 variables for multiple things

b.) any programmer that knows nothing about code(read: you after couple months/years) will have a much more difficult time grasping the code.

The lower function snippet can be expressed as:

var dataListByCode = addBeforeEntriesArray(addDivideData(dataListByCode), invNumber, matterNumber, client, workType);

which is not that problematic. The breaking up of functions is useless in this case, and if you have many inline function chains that is usually sign that you need to rethink the object/function design.