How to replace variable's name with a string in .js file?

Question

I want to refer to a variable by another variable. 1st variable's value is a string equal to 2nd variable's name. How to do, say:

var1 = "var2";
var2 = [1,2,3];

console.log(var1[0]);

and get 1 instead of 'v'?

my code:

localStorage.setItem('scn', 'AR1');

var AR1 = [1,3,4,6];
var AR2 = [1,3,5,6];
var AS2 = [1,3,7,8,9,10];

here_idx = localStorage.getItem('scn').indexOf(1);

In this case here_idx is equal to 2 instead of 0.

I tried parsing it with an error. I don't know how to even search for such problem online. I tried.

Try in the same scope where you initialized var1: [var1][0]

Kai Lehmann
– Kai Lehmann

2020-07-14 21:32:57 +00:00
Commented Jul 14, 2020 at 21:32 — Kai Lehmann
– Kai Lehmann, Commented Jul 14, 2020 at 21:32

imvain2 · Accepted Answer · 2020-07-14 22:10:11Z

3

You can use window[varname] to get a previously declared variable with var (not let or const) that is in the window scope.

Fiddle Since Snippets don't allow localstorage: https://jsfiddle.net/o27andcx/

var AR1 = [1,3,4,6];
var AR2 = [1,3,5,6];
var AS2 = [1,3,7,8,9,10];

localStorage.setItem('scn', 'AR1');

here_var = localStorage.getItem('scn');

here_idx = window[here_var];

console.log(here_idx);

edited Jul 14, 2020 at 22:10

answered Jul 14, 2020 at 21:33

imvain2

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3 Comments

Lionel Rowe Over a year ago

Note that this will only work for variables declared with var, not those declared with let or const. If you want to make a variable global, it's usually clearer to declare it explicitly as a property of window: window.AR1 = ... etc.

Warxuaroz Over a year ago

Doesn't work for me. Results in the same case as in my code.

imvain2 Over a year ago

@Warxuaroz that code does work here is a fiddle: jsfiddle.net/o27andcx So you must not being using it right or your code example doesn't show what you are actually doing

sonEtLumiere · Accepted Answer · 2020-07-14 21:31:43Z

0

You can assign variables from arrays with destructured assignment

const [z, x, ,y] = [1, 2, 3, 4, 5, 6];
console.log(z, x, y);     //Outputs [1, 2, 4]

answered Jul 14, 2020 at 21:31

sonEtLumiere

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1 Comment

Warxuaroz Over a year ago

Would you expand this answer? I have no idea what happend here.

smartdroid · Accepted Answer · 2020-07-14 21:34:46Z

0

"var2" and var2 are not the same. You can do something like the following

var1 = var2;
var2 = [1,2,3];

console.log(var1[0]); // outputs 1 not 'v'

or

var AR1 = [1,3,4,6];
localStorage.setItem('scn', AR1);

here_idx = localStorage.getItem('scn').indexOf(1);//outputs 0

answered Jul 14, 2020 at 21:34

smartdroid

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3 Comments

Warxuaroz Over a year ago

That would work, but I need to keep var1 and var2 unchanged for later use.

smartdroid Over a year ago

Unless you change them variables will remain unchanged. So unsure what the issue is. What is the use case for assigning a variable name as string?

Warxuaroz Over a year ago

I'm following a scenario named AR1, which I want to know in every .html during the scenario, hence I store it in localStorage under 'scn'. I need to also know, where to go with my 'back' and 'next' buttons, hence the AR1 array with all the .htmls' names.

Mohsen Alyafei · Accepted Answer · 2020-07-14 21:32:27Z

-1

One way to do it. But not recommended is as follows: (using eval() ).

It is fully legal and valid though:

var2 = [1,2,3];
var1 = eval("var2");
console.log(var1[0]);

answered Jul 14, 2020 at 21:32

Mohsen Alyafei

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3 Comments

Ravi Kukreja Over a year ago

Using eval is not recommeded. See this

Mohsen Alyafei Over a year ago

I did say that already in my answer. But it is not illegal or invalid as it is fully supported. It is not a deprecated keyword.

Warxuaroz Over a year ago

It's the only suggested answer, that works in my case. Thank you

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