defineReadOnly( obj, propertyMap )

Defines each key-value pair from the property map that you provide as an enumerable property on the target object - but one that cannot be changed or deleted.

Examples

const defineReadOnly = require( "@geronimus/define-read-only" );

const permanentRecord = {};

defineReadOnly(
  permanentRecord,
  {
    taxYear1929FilingDate: "1930-02-28",
    taxYear1930FilingDate: "1931-05-30"
  }
);

// Each property remains enumerable:
Object.keys( permanentRecord ); // => [ "taxYear1929FilingDate", "taxYear1930FilingDate" ]

// You cannot update them:
permanentRecord.taxYear1930FilingDate = "1931-03-31";
permanentRecord.taxYear1930FilingDate; // => "1931-05-30"

// You cannot delete them:
delete permanentRecord.taxYear1930FilingDate; // => false
permanentRecord.taxYear1930FilingDate; // => "1931-05-30"

Parameters

obj object

The object to which the read-only, enumerable properties will be added. It must not be frozen.

propertyMap object

An ordinary object containing one or more key-value pairs to add to the target object.

As well as value properties, you can also define getter and setter functions.

Notes

• Values from the propertyMap that are not primitive values (eg, objects ) will be added by reference. They will not be deep copies.
• Each property added will be enumerable, but not writable or configurable.
• The motivation for this function is to be able to easily add a list of immutable-yet-enumerable properties to an object. (Properties added with Object.defineProperty or Object.defineProperties are not enumerable by default.)
• For example, you can use it to add a "public interface" of methods and getter/setter properties to a constructor function's this reference, after calling the constructor function with the new keyword.