Javascript Concatenate Strings based on conditions

Question

Is there a good way to accomplish this Javascript?

Basically I want something where the values of the fields are concatenate into a single field with comma between the values. Figure something simple like this

var a
var b
var c

allfieldvalue = a + ","b + ","c

My issue is I need to build condition in order for them to be put into allfieldvalue. So if var a = true, var b = false, and var c = true, then allfieldvalue = a +","c. Keep in mind, there could 20 different var. Hopefully that makes sense.

Don't use separate variables. Put them in an array and filter() to get all the true values. Then use .join() to concatenate them. — Barmar
– Barmar, Commented Aug 22, 2022 at 21:46

danh · Accepted Answer · 2022-08-22 21:59:32Z

2

In case the goal is a string containing the names of variables that are true, use this approach:

Make the variables into object props...

var a = true;
var b = false;
var c = true;

let object = { a, b, c };  // produces { a: true, b: false, c: true }

Filter that object to exclude false values:

object = Object.fromEntries(
  Object.entries(object).filter(([k,v]) => v) // produces { a: true, c: true }
)

Concat the keys:

let string = Object.keys(object).join(',');  // produces "a,c"

Demo

var a = true;
var b = false;
var c = true;

let object = { a, b, c }; 

object = Object.fromEntries(
  Object.entries(object).filter(([k,v]) => v) 
)

let string = Object.keys(object).join(','); 
console.log(string)

answered Aug 22, 2022 at 21:59

danh

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1 Comment

JinLe950 Over a year ago

This is actually what I wanted. Based on field value condition being true, put all the variable name into one field. This is only my 3rd day of trying to learn Javascript and didn't even know these option. Thanks!

Barmar · Accepted Answer · 2022-08-22 21:48:11Z

2

Put them in an array, then use .filter() and .join() to concatenate the true values.

let a = true;
let b = false;
let c = true;

let all_vars = [a, b, c];
let result = all_vars.filter(e => e).join(',');
console.log(result);

answered Aug 22, 2022 at 21:48

Barmar

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2 Comments

danh Over a year ago

Produces 'true, true' which I think (I might be wrong) isn't the OP's intent. I think the OP wants 'a,c', which would suggest placing the vars in an object and filtering entires

Barmar Over a year ago

That's what I suspect as well, but the question isn't clear about it.

Charlo Poitras · Accepted Answer · 2022-08-22 21:49:26Z

0

First, It depends on what's in the variable, if you want a boolean and display it, you could do something like this :

function myFunc(...variables) {    
    console.log(variables.filter(v => v != false).join(", "));
}
let a = true;
let b = false;
let c  = true
console.log(myFunc(a,b,c));

answered Aug 22, 2022 at 21:49

Charlo Poitras

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