Destructing string array optional parameters in TypeScript?

Question

I need to implement a string concatenate function, the functionality shows below,

function concatenation(original: string, name1?, name2?){
  return original + name1 + name2;
}

However, the question is, there can be more parameters about name; therefore, this is a not a good coding style. I want to change its like shows below.

function concatenation(original: string, name?:[string]){
  return original + ...name1;
}

But in this way, the program will report an error. How could I achieve it?

DecPK · Accepted Answer · 2022-02-15 03:19:24Z

3

You can use rest with join as:

function concatenation(original: string, name1?, name2?) {
  return original + name1 + name2;
}
concatenation('Original', 'Name1', 'Name2', 'Name3');

This can handle any number of string arguments

function concatenation2(...names: string[]) {
  return names.join('');
}

concatenation2('Original', 'Name1', 'Name2', 'Name3');

function concatenation2(...names) {
  return names.join('');
}

console.log(concatenation2('Original', 'Name1', 'Name2', 'Name3'));

answered Feb 15, 2022 at 3:19

DecPK

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Comments

oceanblue · Accepted Answer · 2025-05-07 09:02:21Z

2

Providing your error report first will make it easier to discover your real problem. In this case, you should know that type annotations are from TypeScript and can only be used in .ts relevant environment.

In fact, what your function concatenation do is simply concating multiple string variables, though you tried to distinguish them by name. Since you want to place the strings sequentially as arguments of the function, you could simply use destructuring assignment.

function concatenation(...items) {
    // now `items` is an Array consisting of all the arguments provided.
    return items.join('');
}

concatenation(1, 2, 3) // "123"
concatenation("a", "bcd", "ef", "g", "h") // "abcdefgh"

edited May 7 at 9:02

answered Feb 15, 2022 at 3:34

oceanblue

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Comments

Harsh Mangalam · Accepted Answer · 2022-02-15 04:06:40Z

0

You cannot destructure javascript object with any type of arithmetic operator like ( +, - , etc...).

function concatenation(original: string, names?: [string]) {
  return `${original}${names.split("")}`;
}

concatenation("original", ["name1", "name2", "name3"]);

answered Feb 15, 2022 at 4:06

Harsh Mangalam

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