Typescript 상에서 Object에 Attribute가 존재하는지 체크하는 3가지 방법

1. hasOwnProperty() method

const hero = {

  name: 'Batman'

};

hero.hasOwnProperty('name');     // => true

hero.hasOwnProperty('realName'); // => false

2. in operator

const hero = {

  name: 'Batman'

};

'name' in hero;     // => true

'realName' in hero; // => false

const hero = {

  name: 'Batman'

};

hero.toString; // => function() {...}

'toString' in hero;              // => true

hero.hasOwnProperty('toString'); // => false

3. Comparing with undefined

hero.name;     // => 'Batman'

hero.realName; // => undefined

hero.realName evaluates to undefined because realName property is missing.

Now you can see an idea: you can compare with undefined to determine the existence of the property.

const hero = {

  name: 'Batman'

};

hero.name !== undefined;     // => true

hero.realName !== undefined; // => false