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TTCTheo's Typesafe Cult
Created by KP on 1/7/2023 in #questions
Types for deep merging defaults in TS
export const deepMergeDefaults = <T>(
  defaultObj: {
    [k: string]: unknown;
  },
  passedObj: { [k: string]: unknown }
) => {
  let result: typeof defaultObj = {};

  for (let [key, value] of Object.entries(defaultObj)) {
    if (!passedObj[key as keyof typeof passedObj]) {
      result[key] = value;
      continue;
    }

    if (typeof value === "object" && !Array.isArray(value) && value) {
      result[key] = deepMergeDefaults(
        value as typeof defaultObj,
        passedObj[key as keyof typeof passedObj] as typeof defaultObj
      );
      continue;
    }

    result[key] = passedObj[key];
  }

  return result as T;
};
export const deepMergeDefaults = <T>(
  defaultObj: {
    [k: string]: unknown;
  },
  passedObj: { [k: string]: unknown }
) => {
  let result: typeof defaultObj = {};

  for (let [key, value] of Object.entries(defaultObj)) {
    if (!passedObj[key as keyof typeof passedObj]) {
      result[key] = value;
      continue;
    }

    if (typeof value === "object" && !Array.isArray(value) && value) {
      result[key] = deepMergeDefaults(
        value as typeof defaultObj,
        passedObj[key as keyof typeof passedObj] as typeof defaultObj
      );
      continue;
    }

    result[key] = passedObj[key];
  }

  return result as T;
};
Similar to lodash's merge defaults, the above function deep merges optional fields by using a default object. What I want is to be able to input an object with type 
type ContainerCustom = {
  position?: {
    left?: keyof typeof CONTAINER_PROPS["position"]["left"];
    top?: keyof typeof CONTAINER_PROPS["position"]["top"];
  };
  padding?: typeof CONTAINER_PROPS["padding"];
};
type ContainerCustom = {
  position?: {
    left?: keyof typeof CONTAINER_PROPS["position"]["left"];
    top?: keyof typeof CONTAINER_PROPS["position"]["top"];
  };
  padding?: typeof CONTAINER_PROPS["padding"];
};
and get back an object with type 
type ContainerCustom = {
  position: {
    left: keyof typeof CONTAINER_PROPS["position"]["left"];
    top: keyof typeof CONTAINER_PROPS["position"]["top"];
  };
  padding: typeof CONTAINER_PROPS["padding"];
};
type ContainerCustom = {
  position: {
    left: keyof typeof CONTAINER_PROPS["position"]["left"];
    top: keyof typeof CONTAINER_PROPS["position"]["top"];
  };
  padding: typeof CONTAINER_PROPS["padding"];
};
1 replies
TTCTheo's Typesafe Cult
Created by KP on 1/5/2023 in #questions
Typescript doesn't show which prop should be provided
3 replies
TTCTheo's Typesafe Cult
Created by KP on 1/2/2023 in #questions
Correct way to tell typescript object's index is not undefined when mapping over keys ?
4 replies