Skip to main content
The Deno 2 Release Candidate is here
Learn more

TypeInfo

Note: This has only been testet server-side with Deno V8

This package provides Extended Type Detection for an instantiated javascript object. The getTypes() function traverses a single- or multi-level user defined object and returns another object showing the inferred types. The detected javascript data types are:

  • symbol
  • string
  • number
  • bigint
  • Date
  • boolean
  • Regexp
  • object
  • Array, including typed arrays like Int16Array
  • function
  • null
  • undefined

as well as:

  • User defined classes

You should Note:

  • This implementation uses Object.getPrototypeOf(obj).constructor.name when dealing with classes, a field that has not always been present in the past, as well as the V8 parameter Object.getOwnPropertyDescriptor(obj, 'name').value, which used to be called storeName and thus may as well be subject to change in the future.
  • Since the data type lookup is done on an instantiated javascript object you will have to initialize the object with values that allow for detection of the type - ‘null’ and ‘undefined’ are by definition not very telling. In the same vain, it is not possible to assign multiple types to an object key.
  • Some types like ‘enum’ in the TypeScript example below, as well all other non-primitive TypeScript types, are not detectable once compiled to javascript, and only the assigned value type can be found.
  • User defined classes are detected.

Given an instantiated object (the complete file can be found in the ‘./examples’ directory):

import { getTypes } from "../mod.ts"
(...)
const employee  = {
    recId: Symbol('REC-ID'),
    employeeNumber: BigInt(9007199254740991),
    lastName: "Hope",
    firstName: "Bob",
    extension: "A",
    email: "bob.hope@heaven.com",
    officeCode: undefined,
    reportsTo: null,
    jobTitle: "BS Manager",
    hired: new Date(2018, 11, 24, 10, 33, 30, 0),
    active: true,
    regexp: /^.*XXX.*$/,
    tools: ['pen', 10, Symbol('ARR-ID')],
    scoreText: DirectionText.Up,
    image: new Image('Office'),
    image2: new Image2('Cubicle'),
    images: [ new Image('Table'),  new Image2('Computer') ]
}

const dataTypes = getTypes('Employee', employee)
console.log(JSON.stringify(dataTypes, undefined, 2))

The call format is getTypes('Employee', employee, false) and the arguments are:

  1. name: Your name for the type object
  2. obj: The object to infer types from
  3. flatten: if set to true the returned object will be flattened (the default is ‘false’).

Try running the example: 

deno run ./examples/typeInfo.ts

produces the following output, where you should note:

  • The resulting object will have the same nesting as the original.
  • Even though the enum type is not detected, the correct type of the value assigned is found
  • For an Array with multiple types are assigned, these types are correctly listed
  • User defined classes are listed
{
  "name": "Employee",
  "type": "object",
  "props": {
    "recId": {
      "desc": "Rec Id",
      "type": "symbol"
    },
    "employeeNumber": {
      "desc": "Employee Number",
      "type": "bigint"
    },
    "lastName": {
      "desc": "Last Name",      
      "type": "string"
    },
    "firstName": {
      "desc": "First Name",     
      "type": "string"
    },
    "extension": {
      "type": "string"
    },
    "email": {
      "type": "string"
    },
    "officeCode": {
      "desc": "Office Code",
      "type": "undefined"
    },
    "reportsTo": {
      "desc": "Reports To",
      "type": "null"
    },
    "jobTitle": {
      "desc": "Job Title",
      "type": "string"
    },
    "hired": {
      "type": "Date",
      "props": {}
    },
    "active": {
      "type": "boolean"
    },
    "regexp": {
      "type": "RegExp",
      "props": {}
    },
    "tools": {
      "type": "Array",
      "props": {
        "0": {
          "type": "string"
        },
        "1": {
          "type": "number"
        },
        "2": {
          "type": "symbol"
        }
      }
    },
    "scoreText": {
      "desc": "Score Text",
      "type": "string"
    },
    "image": {
      "type": "Image",
      "props": {
        "name": {
          "type": "string"
        },
        "format": {
          "type": "string"
        }
      }
    },
    "image2": {
      "desc": "Image 2",
      "type": "Image2",
      "props": {
        "name": {
          "type": "string"
        },
        "format": {
          "type": "string"
        },
        "score": {
          "type": "number"
        }
      }
    },
    "images": {
      "type": "Array",
      "props": {
        "0": {
          "type": "Image",
          "props": {
            "name": {
              "type": "string"
            },
            "format": {
              "type": "string"
            }
          }
        },
        "1": {
          "type": "Image2",
          "props": {
            "name": {
              "type": "string"
            },
            "format": {
              "type": "string"
            },
            "score": {
              "type": "number"
            }
          }
        }
      }
    }
  }
}

Calling getTypes('Employee', employee, true) will return:

{
  "name": "Employee",
  "type": "object",
  "props.recId.desc": "Rec Id",
  "props.recId.type": "symbol",
  "props.employeeNumber.desc": "Employee Number",
  "props.employeeNumber.type": "bigint",
  "props.lastName.desc": "Last Name",
  "props.lastName.type": "string",
  "props.firstName.desc": "First Name",
  "props.firstName.type": "string",
  "props.extension.type": "string",
  "props.email.type": "string",
  "props.officeCode.desc": "Office Code",
  "props.officeCode.type": "undefined",
  "props.reportsTo.desc": "Reports To",
  "props.reportsTo.type": "null",
  "props.jobTitle.desc": "Job Title",
  "props.jobTitle.type": "string",
  "props.hired.type": "Date",
  "props.hired.props": {},
  "props.active.type": "boolean",
  "props.regexp.type": "RegExp",
  "props.regexp.props": {},
  "props.tools.type": "Array",
  "props.tools.props.0.type": "string",
  "props.tools.props.1.type": "number",
  "props.tools.props.2.type": "symbol",
  "props.scoreText.desc": "Score Text",
  "props.scoreText.type": "string",
  "props.image.type": "Image",
  "props.image.props.name.type": "string",
  "props.image.props.format.type": "string",
  "props.image2.desc": "Image 2",
  "props.image2.type": "Image2",
  "props.image2.props.name.type": "string",
  "props.image2.props.format.type": "string",
  "props.image2.props.score.type": "number",
  "props.images.type": "Array",
  "props.images.props.0.type": "Image",
  "props.images.props.0.props.name.type": "string",
  "props.images.props.0.props.format.type": "string",
  "props.images.props.1.type": "Image2",
  "props.images.props.1.props.name.type": "string",
  "props.images.props.1.props.format.type": "string",
  "props.images.props.1.props.score.type": "number"
}