JSONAta expression can be created that ends up in mutation of original input object

[adamscybot]

As discussed here $clone is an internal that is used to ultimately provide an external interface that has no side effects.

$clone was put in the environment so it can be customised, but I'm not sure if this was intended just as a binding from the outside or if it was accepted it could be used inside expression.

One can manipulate the $clone method in order to manipulate the original input object. I feel the original input object should probably never be touched and it is surprising there is a way to get JSONata to alter the input object.

const expression = jsonata(`
 (
    $clone := function($a) {
      $a
    };
    (
      $ ~> | $ | {'newKey': 'this is added to the original input object!'} |
    )
  )
`)

const input = {
  existingKey: 'existing key',
}

console.log('ORIGINAL INPUT BEFORE EXPRESSION', input)
console.log('OUTPUT', await expression.evaluate(input))
console.log('ORIGINAL INPUT AFTER EXPRESSION', input)

In this example, the last console line does show that the newKey has actually been added to the original input object.