What is meant by contextual typing?

1.	What is meant by contextual typing?
Answer» When the TypeScript compiler USES the location (or context) of a variable to infer its type, it’s called CONTEXTUAL typing. In the following example, TypeScript uses the Window.onmousedown function type information to infer the type of the function expression on the right-hand side of the assignment. This allows it to infer the type of the e parameter, which does have a button property but not a property NAMED foo. window.onmousedown = function (e) {console.log(e.button); //<- OKconsole.log(e.foo); //<- ERROR!};

Answer»

When the TypeScript compiler USES the location (or context) of a variable to infer its type, it’s called CONTEXTUAL typing.

In the following example, TypeScript uses the Window.onmousedown function type information to infer the type of the function expression on the right-hand side of the assignment. This allows it to infer the type of the e parameter, which does have a button property but not a property NAMED foo.

window.onmousedown = function (e) {console.log(e.button); //<- OKconsole.log(e.foo); //<- ERROR!};

Discussion

No Comment Found

Related InterviewSolutions

List some of the utility types provided by TypeScript and explain their usage.
What is the Function type in TypeScript?
What are conditional types? How do you create them?
Explain the concept of inheritance in TypeScript.
What are template literal types?
What are string literal types?
What are the ‘implements’ clauses in TypeScript?
Explain the purpose of the ‘in’ operator.
What are triple-slash directives?
What is a type declaration file?