In Typescript, the operator satisfies is used as way to check whether a type satisfies an interface or a condition. satisfies makes sure that the properties of a type that are required are met.

Examples

Suppose we want to create an object called newUser which uses two types: Username and Email, which for this example will be limited to three possible values each, and before taking that newUser object and submitting it to the database, we want to check to make sure that the newUser object satisfies the requirement by using both types: Username and Email. Here’s how we would do that:

type Username = "auser" | "buser" | "cuser";
type Email = "auser@company.com" | "buser@company.com" | "cuser@company.com";
type UserInfo = {
  id: number,
  username: Username,
  email: Email
};

const newUser = {
  id: 123,
  username: "auser",
  email: "auser@company.com"
} satisfies userInfo

In the above example, the Typescript compiler would have no issue with that example. Let’s try to change the value of the username property in the newUser object to a username that is different from the three available usernames:

type Username = "auser" | "buser" | "cuser";
type Email = "auser@company.com" | "buser@company.com" | "cuser@company.com";
type UserInfo = {
  id: number,
  username: Username,
  email: Email
};

const newUser = {
  id: 123,
  username: "duser", //Type '"duser"' is not assignable to type 'Username'.
  email: "auser@company.com"
} satisfies userInfo

In this case the Typescript compiler gives us the above error and therefore the object does not satisfy the type userInfo.

We can also use satisfies along with a utility type. For example, if we want to exclude the property id in the anotherUser object, we would do the following:

const anotherUser = {  
  username: "auser",
  email: "auser@company.com"
} satisfies Omit<UserInfo, "id">

In the above example, the Typescript compiler would accept this without errors.