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JavaScript Utils

The ServiceStack.Text JSON Serializers are only designed for serializing Typed POCOs, but you can still use it to deserialize dynamic JSON but you’d need to specify the Type to deserialize into on the call-site otherwise the value would be returned as a string.

A more flexible approach to read any arbitrary JavaScript or JSON data structures is to use the high-performance and memory efficient JSON utils in ServiceStack Templates implementation of JavaScript.


The Templates JSON and JS Utils are available from the ServiceStack.Common NuGet package:

PM> Install-Package ServiceStack.Common

Which will enable access to the JSON API which preserves the Type which can be used to parse JavaScript or JSON literals:

JSON.parse("1")      //= int 1 
JSON.parse("1.1")    //= double 1.1
JSON.parse("'a'")    //= string "a"
JSON.parse("{a:1}")  //= new Dictionary<string, object> { {"a", 1 } }

It can be used to parse dynamic JSON and any primitive JavaScript data type. The inverse API of JSON.stringify() is also available.


Eval is useful if you want to execute custom JavaScript functions, or if you want to have a text DSL or scripting language for executing custom logic or business rules you want to be able to change without having to compile or redeploy your App. It uses Templates Sandbox which lets you evaluate the script within a custom scope that defines what functions and arguments it has access to, e.g:

public class CustomFilter : TemplateFilter
    public string reverse(string text) => new string(text.Reverse().ToArray());

var scope = JS.CreateScope(
         args: new Dictionary<string, object> { { "arg", "value"} }, 
    functions: new CustomFilter());

JS.eval("arg", scope)                                        //= "value"
JS.eval("reverse(arg)", scope)                               //= "eulav"
JS.eval("itemsOf(3, padRight(reverse(arg), 8, '_'))", scope) //= ["eulav___", "eulav___", "eulav___"]

//= { a: ["eulav___", "eulav___", "eulav___"] }
JS.eval("{a: itemsOf(3, padRight(reverse(arg), 8, '_')) }", scope)