TypeScript type different String vs string All In One

String / string

/*
function checkObjectKeyExist(object: Object, key: String): Boolean {
  return key in object;
}
// The left - hand side of an 'in' expression must be a private identifier or of type 'any', 'string', 'number', or 'symbol'.ts(2360)

*/

// function checkObjectKeyExist(object: Object, key: String): Boolean {
//   return "key" in object;
// }

function checkObjectKeyExist(object: Object, key: string): Boolean {
  return key in object;
}

console.log(checkObjectKeyExist({
  name: "xgqfrms",
  age: 23,
}, "name"));

https://stackoverflow.com/questions/14727044/typescript-difference-between-string-and-string

Object vs object

class SVGStorageUtils {
  // Object
  store: Object;
  // object
  constructor(store: object) {
    this.store = store;
  }
  // string primitive
  setData(key: string = ``, data: object) {
    sessionStorage.setItem(key, JSON.stringify(data));
  }
  // String Object
  getData(key: String = ``) {
    const obj = JSON.parse(sessionStorage.getItem(key));
  }
  clear(key: any) {
    delete this.store[key];
  }
  clearAll() {
    this.store = {};
  }
  init() {
    this.store = {};
  }
}

TypeScript: String vs string

Argument of type 'String' is not assignable to parameter of type 'string'.

'string' is a primitive, but 'String' is a wrapper object.

Prefer using 'string' when possible.

demo

String Object

// error
class SVGStorageUtils {
  store: object;
  constructor(store: object) {
    this.store = store;
  }
  setData(key: String = ``, data: object) {
    sessionStorage.setItem(key, JSON.stringify(data));
  }
  getData(key: String = ``) {
    const obj = JSON.parse(sessionStorage.getItem(key));
  }
}

string primitive

// ok
class SVGStorageUtils {
  store: object;
  constructor(store: object) {
    this.store = store;
  }
  setData(key: string = ``, data: object) {
    sessionStorage.setItem(key, JSON.stringify(data));
  }
  getData(key: string = ``) {
    const obj = JSON.parse(sessionStorage.getItem(key));
  }
}

refs

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