typescript unconventional syntax for object types

Question

typescript unconventional syntax for object types

As I was going through the TypeScript handbook, I stumbled upon this example:

interface Shape {
    color: string;
}

interface Square extends Shape {
    sideLength: number;
}

var square = <Square>{};
square.color = "blue";
square.sideLength = 10;

I'm curious about what exactly <Square>{} means. It seems like a strange syntax to me. Coming from a Java/C# background, it resembles a generic for an anonymous object. Can you explain what it is and what limitations there are when creating objects in this way?

javascript object syntax typescript

Answer 1

Answer №1

When working with TypeScript, the concept of "casting" involves interpreting an empty object literal ({}) as a Square in this context. By doing so, the TypeScript compiler will automatically infer that the square variable is of type Square, and Intellisense will provide accurate member suggestions.

It's important to remember that this process is not true casting in the traditional sense, since types are ultimately abstract concepts within TypeScript. The handling of types is primarily for the benefit of the compiler rather than actual runtime operations.

Answer 2

When working with TypeScript, the concept of "casting" involves interpreting an empty object literal ({}) as a Square in this context. By doing so, the TypeScript compiler will automatically infer that the square variable is of type Square, and Intellisense will provide accurate member suggestions.

It's important to remember that this process is not true casting in the traditional sense, since types are ultimately abstract concepts within TypeScript. The handling of types is primarily for the benefit of the compiler rather than actual runtime operations.

Answer 3

Answer №2

Have you heard of a Type Assertion before? Check it out here

Here is the pattern you're interested in:

var square = <Square>{};
square.color = "blue";
square.sideLength = 10;

This technique is commonly used (though not recommended) for transitioning from JavaScript to TypeScript, especially for lazy object initialization. Learn more about it here

Answer 4

Have you heard of a Type Assertion before? Check it out here

Here is the pattern you're interested in:

var square = <Square>{};
square.color = "blue";
square.sideLength = 10;

This technique is commonly used (though not recommended) for transitioning from JavaScript to TypeScript, especially for lazy object initialization. Learn more about it here

typescript unconventional syntax for object types

Answer №1

Answer №2

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