# The prefix `++` operator

## Returns correct result when used on a `Number`

### Juttle

    function f(x) {
      var y = ++x;

      return [x, y];
    }

    emit -from Date.new(0) -limit 1 | put result = f(5) | view result

### Output

    { "time": "1970-01-01T00:00:00.000Z", result: [6, 6] }

## Produces an error when used on operand of invalid type

### Juttle

    function f(x) {
      var y = ++x;
    }

    emit -from Date.new(0) -limit 1 | put result = f(null) | view result

### Warnings

  * "++" operator: Invalid operand type (null).