At the time of writing, json-logic-engine is approximately 90% compatible with json-logic-js's test suite, this is unlikely to improve due to differences of opinion between the authors & language origins.

json-logic-js was developed to be compatible with PHP, and this has led to some subtle differences.

Empty Arrays are Truthy

In JavaScript & most languages, because arrays are objects, they are evaluated as truthy even if they are empty. json-logic-engine follows this convention.

Because PHP does not follow this convention, the author of json-logic-js wrote his interpreter to evaluate [] as false, as well as a few comparable cases, like [0]. I do not think I will budge on this stance, but it is possible to override the and, or and if methods to mimic this functionality if necessary.

No Support for "if" chaining

This may be adjusted at some point in the future, json-logic-engine supports if statements in the following format:
{
    "if": [
        conditional,
        then,
        else
    ]
}
It does not support the syntax 
{
    "if": [
        conditional,
        then,
        conditional2,
        then2,
        ...,
        else
    ]
}
This may change in the future.

"all" with zero items evaluates to true

To keep in line with JavaScript's every method, which checks if each item in an array checked against a conditional is true, if there are zero items in the array the method defaults to true.
{
    "all": [[], { "var": "" }]
} 
// json-logic-js: false
// json-logic-engine: true

Conclusion

For most users, it is the author's opinion that most will not be impacted by the differences between the two modules.