0function greet(this: {name: string}, greeting: string) { return `${greeting}, ${this.name}`; } type ThisType = ThisParameterType<typeof greet>; type NoThis = OmitThisParameter<typeof greet>; const obj: ThisType = {name: "Alice"}; const greetNoThis: NoThis = greet.bind(obj); console.log(greetNoThis("Hello"));
| Step | Action | Evaluation | Result |
|---|---|---|---|
| 1 | Define function greet with 'this' parameter | Function greet(this: {name: string}, greeting: string) | Function created |
| 2 | Extract 'this' type using ThisParameterType<typeof greet> | ThisParameterType<typeof greet> | {name: string} |
| 3 | Extract function type without 'this' using OmitThisParameter<typeof greet> | OmitThisParameter<typeof greet> | (greeting: string) => string |
| 4 | Create object obj of type {name: string} | obj = {name: "Alice"} | obj created |
| 5 | Bind greet to obj to create greetNoThis | greet.bind(obj) | Function greetNoThis(greeting: string) |
| 6 | Call greetNoThis("Hello") | greetNoThis("Hello") | "Hello, Alice" |
| 7 | Output result | console.log output | Hello, Alice |
| Variable | Start | After Step 4 | After Step 5 | After Step 6 | Final |
|---|---|---|---|---|---|
| greet | function with 'this' param | unchanged | unchanged | unchanged | unchanged |
| ThisType | undefined | {name: string} | {name: string} | {name: string} | {name: string} |
| NoThis | undefined | (greeting: string) => string | (greeting: string) => string | (greeting: string) => string | (greeting: string) => string |
| obj | undefined | {name: "Alice"} | {name: "Alice"} | {name: "Alice"} | {name: "Alice"} |
| greetNoThis | undefined | undefined | function bound to obj | function bound to obj | function bound to obj |
| result | undefined | undefined | undefined | "Hello, Alice" | "Hello, Alice" |
ThisParameterType<T> extracts the type of 'this' from a function type T. OmitThisParameter<T> creates a function type like T but without the 'this' parameter. Use ThisParameterType to get the 'this' object type. Use OmitThisParameter to call functions without binding 'this' explicitly. Useful for safer typings and flexible function calls.
What does ThisParameterType do in TypeScript?
ThisParameterTypethis parameter from a function type if it exists.OmitThisParameter removes the this parameter, but ThisParameterType extracts it instead.this from a function type -> Option BThisParameterType extracts this type [OK]this parameterWhich of the following is the correct syntax to use OmitThisParameter on a function type fn?
type NewFn = ?
OmitThisParameter is a generic type, so it requires angle brackets with a type inside, like <typeof fn>.typeof fn to get the function type.Consider this TypeScript code:
function greet(this: { name: string }, greeting: string) {
return `${greeting}, ${this.name}!`;
}
type GreetNoThis = OmitThisParameter<typeof greet>;
const greetNoThis: GreetNoThis = (greeting) => greet.call({ name: 'Alice' }, greeting);
console.log(greetNoThis('Hello'));What is the output?
OmitThisParameter effectthis parameter from greet, so greetNoThis only takes greeting.greetNoThis calls greet.call with an explicit this object having name: 'Alice', so the greeting uses 'Alice'.this, call sets it explicitly [OK]this, call sets it manually [OK]this is undefined inside greetthis parameterFind the error in this TypeScript code using ThisParameterType:
function show(this: { id: number }) {
console.log(this.id);
}
type ShowThis = ThisParameterType<typeof show>;
const idValue: ShowThis = 5;ThisParameterType outputthis type, which is { id: number } here, not a number.5 (a number) to ShowThis (an object type) causes a type error.ShowThis is incorrect -> Option Athis type matches assigned value [OK]ThisParameterType returns a primitivethis parameter presenceYou have a method with a this parameter and want to create a version without this that can be called with just the normal arguments. Which TypeScript utility types would you combine to extract the this type and create a new function type without this?
this typeThisParameterType extracts the this type from the method.this parameterOmitThisParameter creates a new function type without the this parameter.ThisParameterType to get this type and OmitThisParameter to remove this -> Option Cthis for safe function types [OK]this first, then omit it for new function type [OK]this before extracting itPass the test and this pattern moves unknown strong while earning +1 Grip toward your certificate.