@nozbe/watermelondb/decorators/lazy/index.js

Build powerful React Native and React web apps that scale from hundreds to tens of thousands of records and remain fast

"use strict";

exports.__esModule = true;
exports.default = lazy;
// Defines a property whose value is evaluated the first time it is accessed
// For example:
//
// class X {
//   @lazy date = new Date()
// }
//
// `date` will be set to the current date not when constructed, but only when `xx.date` is called.
// All subsequent calls will return the same value
function lazy(target, key, descriptor) {
  var {
    configurable: configurable,
    enumerable: enumerable,
    initializer: initializer,
    value: value
  } = descriptor;
  return {
    configurable: configurable,
    enumerable: enumerable,
    get: function () {
      // $FlowFixMe
      var that = this;
      // This happens if someone accesses the
      // property directly on the prototype
      if (that === target) {
        return undefined;
      }
      var returnValue = initializer ? initializer.call(that) : value;

      // Next time this property is called, skip the decorator, and just return the precomputed value
      Object.defineProperty(that, key, {
        configurable: configurable,
        enumerable: enumerable,
        writable: true,
        value: returnValue
      });
      return returnValue;
    } // TODO: What should be the behavior on set?
  };
}

// Implementation inspired by lazyInitialize from `core-decorators`