append string to string array if not array yet

Question

I want to create a array of strings by appending, but it matters if the origin is an array or yet a string. Therefore I need to convert a string like "abc" to a string array.

if I use

Array.from()

it makes me something like this ["a","b","c"] but I want to have ["abc"];

Is there a easy way that takes an input like "abc" and at the same time ["a","abc"] I so that I can append later one one more string with push for example?

some constraints: I cannot create

let a = [];

because it is coming from extern. And sure, I can add some code to check what is its, but I search for a simple mechanism.

I think i need something like arr1.flat();

i don't see why you don't just use [string] instead of Array.from() — Nils Schwebel
– Nils Schwebel, Commented Feb 6, 2022 at 12:48
if you want to have controle over all entries you could do something like: array.reduce((array, entry) => [(array[0] ?? '') + entry], ''); — Jens Ingels
– Jens Ingels, Commented Feb 6, 2022 at 12:50
Lastly with simply concats at the same level you could do [array.join('')]. Good luck — Jens Ingels
– Jens Ingels, Commented Feb 6, 2022 at 12:57

picklepick · Accepted Answer · 2022-02-06 14:23:30Z

2

I'm not quite sure if I understand your question correctly, you want to either append the source to an existing array if it's a string or concatenate the source if it's already an array?

Have you tried typeof? See the MDN typeof docs

if (typeof origin === 'string') {
   mylist.push(origin)
} else {
   mylist = mylist.concat(origin)
}

EDIT: As per NiceBooks comment:

let str = new String('Hello, world')
typeof str // 'object'

(source)

Therefore, as they suggested the following might be better:

if (Array.isArray(origin)) {
   mylist = mylist.concat(origin) // there are more cleaner ways, for starters this should be fine
} else {
   mylist.push(origin)
}

edited Feb 6, 2022 at 14:23

answered Feb 6, 2022 at 12:52

picklepick

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2 Comments

Nice Books Over a year ago

Using typeof isn't a 100% solution to check if a variable is a String (typeof of strings created through the String constructor is object). On the other hand Array.isArray(origin) is the best way to check if a variable is an Array.

picklepick Over a year ago

@NiceBooks Interesting, I didn't know that. I'll look into it and add it to my answer. Thanks.

Carsten Massmann · Accepted Answer · 2022-02-06 16:26:48Z

1

Maybe this does what you want:

function strArr(base,s){
 return !Array.isArray(base)?[base,s]:[...base,s];
}

let a="abc", arr=["one","two"];

console.log(strArr(a,"b"));
console.log(strArr(arr,"three"));

I changed my answer slightly. Now the input array base will not be changed anymore by the function.

edited Feb 6, 2022 at 16:26

answered Feb 6, 2022 at 13:16

Carsten Massmann

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