Changing the names of the remaining variables while object destructuring in TypeScript

Question

Changing the names of the remaining variables while object destructuring in TypeScript

UPDATE:

I have created an issue regarding this topic on github: https://github.com/Microsoft/TypeScript/issues/21265
It appears that the syntax { ...other: xother } is not valid in JavaScript or TypeScript, and should not compile.

Initial Query:

Consider the following scenario:

const values = { a: "1", b: "2", c: "3", d: "4" };
const { a: va, b: vb, ...other } = values;

where a new variable name va is assigned to property a.

According to TypeScript specifications, is it permissible to do the same with the remaining properties using ...other? Like so:

const { a: va, b: vb, ...other: vother } = values;

It has been verified to work (online test). However, I am unable to locate where this behavior is officially specified.

The examples provided in the documentation typically demonstrate property renaming in a more standard manner: TypeScript Handbook - Variable Declarations. The specification grammar references a BindingPattern which may not be clearly defined in the spec: TypeScript Spec.

My initial assumption is that this syntax might not be very practical since ...other already serves as a custom variable name. Nonetheless, it functions as expected. I am intrigued to understand the specific definition behind it or if it is merely a working exception (which I doubt).

javascript typescript destructuring

Answer 1

Answer №1

The link provided in the handbook you mentioned does cover most of the scenarios illustrated in your example regarding destructuring. However, it seems that a particular situation is only implicitly covered and not explicitly outlined.

Specifically, the feature you are highlighting involves the combination of:

Creating a variable for the remaining items in an object using the syntax ...:

as well as

Assigning different names to properties.

While the handbook doesn't provide an example where both aspects are utilized together, it's worth noting that the ...other token in this scenario remains unused and unreferenceable. In the corrected version presented below, excluding the erroneous line, the other token does not appear in the output at all.

Here's a condensed version of the example:

const values = { a: "1", b: "2", c: "3", d: "4" };

const { a: one, ...other: twoThreeFour } = values;

console.log(other); // ERROR no 'other' variable exists
console.log(a, twoThreeFour); // OK

In the error-free version - after transpilation to JavaScript, there is no mention of the other variable throughout the code:

const values = { a: "1", b: "2", c: "3", d: "4" };

const { a: one, ...other: twoThreeFour } = values;

console.log(a, twoThreeFour); // OK

An issue has been raised to enhance the clarity surrounding the use of rest elements in relation to destructuring within the language specification.

Answer 2

The link provided in the handbook you mentioned does cover most of the scenarios illustrated in your example regarding destructuring. However, it seems that a particular situation is only implicitly covered and not explicitly outlined.

Specifically, the feature you are highlighting involves the combination of:

Creating a variable for the remaining items in an object using the syntax ...:

as well as

Assigning different names to properties.

While the handbook doesn't provide an example where both aspects are utilized together, it's worth noting that the ...other token in this scenario remains unused and unreferenceable. In the corrected version presented below, excluding the erroneous line, the other token does not appear in the output at all.

Here's a condensed version of the example:

const values = { a: "1", b: "2", c: "3", d: "4" };

const { a: one, ...other: twoThreeFour } = values;

console.log(other); // ERROR no 'other' variable exists
console.log(a, twoThreeFour); // OK

In the error-free version - after transpilation to JavaScript, there is no mention of the other variable throughout the code:

const values = { a: "1", b: "2", c: "3", d: "4" };

const { a: one, ...other: twoThreeFour } = values;

console.log(a, twoThreeFour); // OK

An issue has been raised to enhance the clarity surrounding the use of rest elements in relation to destructuring within the language specification.

Answer 3

Answer №2

When it comes to destructuring variables, feel free to use any name other than other. Here's an example to demonstrate:

const {...rest} = someVaribale;
const {...myname} = otherVariable;

Answer 4

When it comes to destructuring variables, feel free to use any name other than other. Here's an example to demonstrate:

const {...rest} = someVaribale;
const {...myname} = otherVariable;

Changing the names of the remaining variables while object destructuring in TypeScript

Answer №1

Answer №2

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