in livelooping there is this concept called First Loop, which is setting the tempo based on the time between a start and end point. knowing this could you write me some code for a basic first loop setter in base javascript?
Sure, here's an example of a basic first loop setter in JavaScript that calculates the tempo based on the time between a start and end point:

```javascript
// Get the start and end time in milliseconds
const startTime = Date.now();
// Wait for the user to indicate the end of the loop, for example by clicking a button
// or pressing a key
// Then get the end time in milliseconds
const endTime = Date.now();

// Calculate the time difference in seconds
const timeDiffInSeconds = (endTime - startTime) / 1000;

// Calculate the tempo based on the time difference
// For example, assuming a 4/4 time signature, we could set the tempo to the number of
// beats per minute based on the number of bars (or measures) in the loop
const numberOfBars = 4; // For example, assume a loop of 4 bars
const beatsPerBar = 4; // Assume a 4/4 time signature
const tempo = Math.round(numberOfBars / timeDiffInSeconds * beatsPerBar * 60);

// Display the calculated tempo
console.log(`The tempo is ${tempo} BPM`);
```

Note that this is just an example and you may need to adapt it to fit your specific use case, such as adjusting the time signature, number of bars, or tempo calculation formula. Additionally, you may need to implement additional functionality to handle user input for starting and stopping the loop, or to set the tempo in your looping software.