Having trouble concatenating two strings in TypeScript

Question

I am trying to concatenate two strings in TypeScript like this:

let string1 = new String("IdNumber: " + this.IdNumber);
let string2 = new String(this.notes);
this.notes = string1.concat(string2.toString());

The output I see for this.notes on line 3 is missing the original text from this.notes in string2. This is what I see in devTools for this.notes on line 3 when debugging:

"IdNumber: 524242

"

when hovering over this.notes on line 2 in devTools it looks like this:

"testing

 testing 2

 testing 3"

I was hoping that this.notes on line 3 would look like this:

"IdNumber: 524242

 testing

 testing 2

 testing 3"

What am I doing wrong?

String objects in JavaScript are very rarely useful. They are not the same as string primitive values. — Pointy
– Pointy, Commented Nov 23, 2022 at 14:10
Please provide a self-contained minimal reproducible example that demonstrates your issue when pasted into a standalone IDE. Right now the this context is missing so it's hard to know what's going on. I concur that new String(...) is almost certainly not what you want to do; you could use just String(...) instead. But without being able to reproduce the issue, this is all just guesswork. — jcalz
– jcalz, Commented Nov 23, 2022 at 14:13
It might help if you could explain what you're trying to get that "IdNumber: " + this.IdNumber + this.notes wouldn't give you. — Pointy
– Pointy, Commented Nov 23, 2022 at 14:13
This code may not be good but I just realized that I made a mistake and was setting this.notes in a separate location that was overwriting what was being set here. It was still very helpful to see how to use the template literals instead of String objects. — Rich
– Rich, Commented Nov 23, 2022 at 16:28

jsejcksn · Accepted Answer · 2022-11-23 14:16:42Z

2

I think a more ergonomic (if not idiomatic) approach would be using template literals, for example:

Code in TypeScript Playground

const example = {
  IdNumber: 524242,
  notes: 'testing\n\ntesting 2\n\ntesting 3',
  update () {
    this.notes = `IdNumber: ${this.IdNumber}\n\n${this.notes}`;
  },
};

console.log(example.notes); // "testing\n\ntesting 2\n\ntesting 3"
example.update();
console.log(example.notes); // "IdNumber: 524242\n\ntesting\n\ntesting 2\n\ntesting 3"

answered Nov 23, 2022 at 14:16

jsejcksn

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Dimava · Accepted Answer · 2022-11-23 14:16:55Z

2

For string concatenation it is recommended* to use Template Literals

let string1 = `IdNumber: ${this.IdNumber}`;
let string2 = `${this.notes}`;
this.notes = `${string1}${string2}`

* https://eslint.org/docs/latest/rules/prefer-template

answered Nov 23, 2022 at 14:16

Dimava

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