validate-json.js

angular.module('jsondiff').
service('JsonValidatorService', function() {

    var jvs = this;

    jvs.isJSON = function(obj) {
        // check "obj" for string
        if (typeof obj === "string") {
            // obj is string, parse it using JSON.parse()
            try {
                var isJSON = JSON.parse(obj);
                // this is for null, as "null" is a valid JSON and type of null is object
                // but "null" is itself falsey
                // if isJSON is null then if( isJSON && ... ) will be false
                if (isJSON && typeof isJSON === "object") {
                    // everything goes fine, return true
                    return true;
                }

                return false;
            } catch (e) {
                // cannot parse, invalid JSON
                return false;
            }
        }
        // "obj" is not string, so first,
        // JSON.stringify() it, then parse
        var jsonString = JSON.stringify(obj);
        // now parse this json string
        try {
            var checkJSON = JSON.parse(jsonString);
            // this is for null, as "null" is a valid JSON and type of null is object
            // but "null" is itself falsey
            // if isJSON is null then if( isJSON && ... ) will be false
            if (checkJSON && typeof checkJSON === "object") {
                // everything goes fine, return true
                return true;
            }

            return false;
        } catch (e) {
            // cannot parse, invalid JSON
            return false;
        }
    };

    return jvs;
})