How to escape a string of JSON/JavaScript in iOS.

JavaScriptEncode.swift

extension String {
    func javaScriptEscapedString() -> String {
        // Because JSON is not a subset of JavaScript, the LINE_SEPARATOR and PARAGRAPH_SEPARATOR unicode
        // characters embedded in (valid) JSON will cause the webview's JavaScript parser to error. So we
        // must encode them first. See here: http://timelessrepo.com/json-isnt-a-javascript-subset
        // Also here: http://media.giphy.com/media/wloGlwOXKijy8/giphy.gif
        let str = self
            .stringByReplacingOccurrencesOfString("\u{2028}", withString: "\\u2028")
            .stringByReplacingOccurrencesOfString("\u{2029}", withString: "\\u2029")
        // Because escaping JavaScript is a non-trivial task (https://github.com/johnezang/JSONKit/blob/master/JSONKit.m#L1423)
        // we proceed to hax instead:
        let data = try! NSJSONSerialization.dataWithJSONObject([str], options: [])
        let encodedString = NSString(data: data, encoding: NSUTF8StringEncoding)!
        return encodedString.substringWithRange(NSMakeRange(1, encodedString.length - 2))
    }
}

Hi,
I need to pass the contents of the file attached to a javascript function. Your escape function didn't work :(

Link to the file: https://drive.google.com/file/d/0B_Co3TU_E9CCQlpTSEdSbmF4cXc/view?usp=sharing

Thanks pwightman. This is the version of the code in swift 5

extension String 
{
    func javaScriptEscapedString() -> String 
    {
        // Because JSON is not a subset of JavaScript, the LINE_SEPARATOR and PARAGRAPH_SEPARATOR unicode
        // characters embedded in (valid) JSON will cause the webview's JavaScript parser to error. So we
        // must encode them first. See here: http://timelessrepo.com/json-isnt-a-javascript-subset
        // Also here: http://media.giphy.com/media/wloGlwOXKijy8/giphy.gif
        let str = self.replacingOccurrences(of: "\u{2028}", with: "\\u2028")
                      .replacingOccurrences(of: "\u{2029}", with: "\\u2029")
        // Because escaping JavaScript is a non-trivial task (https://github.com/johnezang/JSONKit/blob/master/JSONKit.m#L1423)
        // we proceed to hax instead:
        let data = try! JSONSerialization.data(withJSONObject:[str], options: [])
        let encodedString = NSString(data: data, encoding: String.Encoding.utf8.rawValue)!
        return encodedString.substring(with: NSMakeRange(1, encodedString.length - 2))
    }
}

swift 5.1

extension String {
    var javaScriptEscapedString: String {
        // Because JSON is not a subset of JavaScript, the LINE_SEPARATOR and PARAGRAPH_SEPARATOR unicode
        // characters embedded in (valid) JSON will cause the webview's JavaScript parser to error. So we
        // must encode them first. See here: http://timelessrepo.com/json-isnt-a-javascript-subset
        // Also here: http://media.giphy.com/media/wloGlwOXKijy8/giphy.gif
        let str = self.replacingOccurrences(of: "\u{2028}", with: "\\u2028")
                      .replacingOccurrences(of: "\u{2029}", with: "\\u2029")
        // Because escaping JavaScript is a non-trivial task (https://github.com/johnezang/JSONKit/blob/master/JSONKit.m#L1423)
        // we proceed to hax instead:
        do {
            let encoder = JSONEncoder()
            let data = try encoder.encode([str])
            let encodedString = String(decoding: data, as: UTF8.self)
            return String(encodedString.dropLast().dropFirst())
        } catch {
            return self
        }
    }
}