Efficient way to have an Array from differing variable type

Question

It's not really a problem, but I like to improve my JavaScript/ES6 skills.

I'm trying to find a more efficient way to always have an array, no matter if my incoming variable has just a single value or an array.

What I'm currently doing is:

var inp;

// just for the showcase
if (Math.random() > 0.5) {
  inp = 'foo';
} else {
  inp = ['foo', 'bar'];
}

// this is what I want to optimize
if (Array.isArray(inp)) {
  outp = inp;
} else {
  outp = [inp];
}

console.log(outp);

I'm not talking just shortening the code at any price, but effiency and maybe elegance.

The real problem is that programmers have spent far too much time worrying about efficiency in the wrong places and at the wrong times; premature optimization is the root of all evil (or at least most of it) in programming. — Liam
– Liam, Commented Apr 24, 2018 at 10:07
Leave it how it is and do something more productive with your time :) — Liam
– Liam, Commented Apr 24, 2018 at 10:08
@Liam I like your thinking and Knuths quote has a lot of truth in it. — Sascha
– Sascha, Commented Apr 24, 2018 at 10:25
Here's another quote for you: Any fool can write code that a computer can understand. Good programmers write code that humans can understand.. In the face of marginal performance gains always pick the option that's the easiest to read — Liam
– Liam, Commented Apr 24, 2018 at 10:31

hsz · Accepted Answer · 2018-04-24 10:08:33Z

4

You can skip this isArray check with using concat:

const outp = [].concat(inp);

It'll always give you an array with elements (not nested):

[].concat('foo')
// ['foo']

[].concat(['foo'])
// ['foo']

answered Apr 24, 2018 at 10:08

hsz

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3 Comments

Sven van de Scheur Over a year ago

Elegant solution

Máté Safranka Over a year ago

If you really badly need to shave off that one line of code, this is the way I guess. Personally I think it might be a bit unintuitive because it's not immediately apparent what this code is supposed to accomplish and why it's even there, which may make it difficult for an outside viewer (or yourself, a few weeks later) to understand. Still, upvoted because it works and does what OP needs :)

Liam Over a year ago

This appears to be less efficient and I'd argue is harder to read.

jancha · Accepted Answer · 2018-04-24 10:13:45Z

3

How about testing it? Here is a jsperf for you: https://jsperf.com/dynamic-array-creation

instanceof seems to be the most efficient way.

answered Apr 24, 2018 at 10:13

jancha

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8 Comments

Liam Over a year ago

Test first optimise later. that said even the slowest can do 7 millions ops a second....You need to ask yourself if that performance gain is really worth it

jancha Over a year ago

Deliberately choosing a solution that is 20x slower is a bad practice. Non optimal code adds up and slows down the performance significantly on slower devices and increases power consumption. Also, if your solution is used by millions of users, that becomes even more important.

Liam Over a year ago

Is this solution used by millions of users? Is this a bottle neck or can you can more bang for your buck somewhere else, like I said premature optimisation is the root of all evil

Liam Over a year ago

Testing is the correct answer though. Everything else is a guess at best

Liam Over a year ago

Ethics are subjective. Any fool can write code that a computer can understand. Good programmers write code that humans can understand..

|

Sven van de Scheur · Accepted Answer · 2018-04-24 10:07:51Z

0

Many approaches are possible. Depending on how accurate you wan't you detection to be. A quick example:

var outp = Array.isArray(inp) ? inp : in[];

Which is nothing more than a shorthand for your code.

You should ask yourself if this is desirable. If you have function that expects an array but gets a string as input. Should it even continue? Many interfaces provide different explicit methods for this. E.g.: add(array) and addOne(string)

answered Apr 24, 2018 at 10:07

Sven van de Scheur

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Comments

gurvinder372 · Accepted Answer · 2018-04-24 10:11:17Z

0

You can concat empty array [] if Math.random is less than 0.5

["foo"].concat( Math.random > 0.5 ? "bar" : [] )

answered Apr 24, 2018 at 10:11

gurvinder372

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