Custom Operations

It's not always practical to add a top-level baked-in method for every possible use case—that's how you end up with PHP. 🙃

But it is possible to build hugely powerful custom methods, and the community has created lots of them. This Wiki is a place to show off, or to link out to larger libraries or longer blog-length discussions.

Temporary Variables

Sometimes, you need some scratch space to re-use a result more than once in your rule. The core JsonLogic implementation has no setters, which helps developers trust customer-provided rules. These operations break that tenet, but in a relatively safe, sandboxed way:

jsonLogic.add_operation("set_temp", function(key, value){
    if( ! this.temp_variables){ this.temp_variables = {}; }
    this.temp_variables[key] = value;
    return value;
});

jsonLogic.add_operation("get_temp", function(key){
    if( ! this.temp_variables){ this.temp_variables = {}; }
    return this.temp_variables[key];
});

Example

This rule tests that a complicated regex matches, and that an optional capture group is empty. (Note, it uses an implementation of index found below)

var rule = {"and":[
    {'!=':[
        null,
        {"set_temp":[
            "match_result",
            {"method":[
                {"var":"a"},
                "match",
                ["(.)(.)(.)?(.)"]
            ]}
        ]}
    ]},
    {"==":[
        null,
        {"index":[
            {"get_temp":"match_result"},
            3
        ]}
    ]}
]};

jsonLogic.apply(rule, {"a": "ab"}); //false, match fails
jsonLogic.apply(rule, {"a": "abc"}); //true, match succeeds, optional capture missing
jsonLogic.apply(rule, {"a": "abcd"}); //false, match succeeds, optional capture present