This JavaScript code creates an array `arr` with elements [1, 2, 3]. It then adds the number 4 to the end of the array using the `push` method. Finally, it prints the updated array `[1, 2, 3, 4]` to the console.
Below is an instruction that describes a task, paired with an input that provides further context. Write a response that appropriately completes the request.

### Instruction:
What does this JavaScript code do?

### Input:
`javascript
let arr = [1, 2, 3];
arr.push(4);
console.log(arr);
`

### Response:
This JavaScript code creates an array `arr` with elements [1, 2, 3]. It then adds the number 4 to the end of the array using the `push` method. Finally, it prints the updated array `[1, 2, 3, 4]` to the console.<|im_end|>