How to combine two SwiftyJSON objects

As you said, swiftyJSON does not have an append functionality.

What you can do is parse the swiftyJSON objects into an array of type anyObject and append them.

let json = JSON(data: data!) 
var JSONObject = JSON(json["content"].arrayObject! + json["content"].arrayObject!)

Data -> NSData Object received from a HTTP request.

extension JSON {
    mutating func merge(other: JSON) {
        for (key, subJson) in other {
            self[key] = subJson
        }
    }

    func merged(other: JSON) -> JSON {
        var merged = self
        merged.merge(other: other)
        return merged
    }
}

I liked the answer of @user2215977, but I also needed merging of nested JSONs. I extended the extension to merge nested JSONs and arrays, whereas arrays containing JSONs aren't merged, but are both in the array of the newly generated JSON.

import SwiftyJSON

extension JSON {
    mutating func merge(other: JSON) {
        if self.type == other.type {
            switch self.type {
                case .dictionary:
                    for (key, _) in other {
                        self[key].merge(other: other[key])
                    }
                case .array:
                    self = JSON(self.arrayValue + other.arrayValue)
                default:
                    self = other
            }
        } else {
            self = other
        }
    }

    func merged(other: JSON) -> JSON {
        var merged = self
        merged.merge(other: other)
        return merged
    }
}

In order to illustrate the usage I'll post my tests for this extension as well.

import XCTest
import SwiftyJSON

class JSONTests: XCTestCase {
    func testPrimitiveType() {
        let A = JSON("a")
        let B = JSON("b")
        XCTAssertEqual(A.merged(other: B), B)
    }

    func testMergeEqual() {
        let json = JSON(["a": "A"])
        XCTAssertEqual(json.merged(other: json), json)
    }

    func testMergeUnequalValues() {
        let A = JSON(["a": "A"])
        let B = JSON(["a": "B"])
        XCTAssertEqual(A.merged(other: B), B)
    }

    func testMergeUnequalKeysAndValues() {
        let A = JSON(["a": "A"])
        let B = JSON(["b": "B"])
        XCTAssertEqual(A.merged(other: B), JSON(["a": "A", "b": "B"]))
    }

    func testMergeFilledAndEmpty() {
        let A = JSON(["a": "A"])
        let B = JSON([:])
        XCTAssertEqual(A.merged(other: B), A)
    }

    func testMergeEmptyAndFilled() {
        let A = JSON([:])
        let B = JSON(["a": "A"])
        XCTAssertEqual(A.merged(other: B), B)
    }

    func testMergeArray() {
        let A = JSON(["a"])
        let B = JSON(["b"])
        XCTAssertEqual(A.merged(other: B), JSON(["a", "b"]))
    }

    func testMergeNestedJSONs() {
        let A = JSON([
            "nested": [
                "A": "a"
            ]
        ])

        let B = JSON([
            "nested": [
                "A": "b"
            ]
        ])

        XCTAssertEqual(A.merged(other: B), B)
    }
}