Convert arrays of strings to one array JS

Just use join(',') and split(','). And further use map() (optional) to remove the trailing and leading whitespaces. This will also ensures that there can be any amount of whitespaces between array element.

let fruitsArry = ['apple', 'apple, mango, orange', 'orange'];
var res = fruitsArry.join(',').split(',').map(item=>item.trim());
console.log(res);

Just join and split with the separator of the quoted part.

let fruitsArray = ['apple', 'apple, mango, orange', 'orange'],
    result = fruitsArray.join(', ').split(', ');
    
console.log(result);

With white space after comma, you could split with optional whitepsace.

let fruitsArray = ['apple', 'apple, mango, orange', 'orange'],
    result = fruitsArray.join().split(/,\s*/);
    
console.log(result);

Without join(" ,") which generates an unnecessary intermediate string, you may do as follows;

var fruitsArry = ['apple', 'apple, mango, orange', 'orange'],
    result     = fruitsArry.reduce((r,e) => r.concat(e.includes(",") ? e.split(/\s*,\s*/)
                                                                     : e),[]);
console.log(result);

let array = ['apple', ' apple , mango , orange ', 'orange'];

newArray = array.join(',').split(/\s*,\s*/);
    
console.log(newArray);

I think this should do the trick. This will handle white space before and after each word too.

To answer your question simply you can use:

const af=a=>a.join(',').split(',').map(e=>e.trim()); // 45 character

and use it like:

let res = af(['apple', 'apple, mango, orange', 'orange']);
console.log(res);

Or if you prefer the long version:

/**
 * Define the function
 */
function formatArray(arr) {
  let tmp: string[];
  let result: string[] = [];

  tmp = arr.join(',').split(',');

  tmp.forEach((el, i) => {
    let str = el.trim();  // this is to remove the extra spaces
    result.push(str); // add the element to final array
  });
  return result;
}

And use it as:

// The orignal array
let arr = ['apple', 'apple, mango, orange', 'orange'];
arr = formatArray(arr);
console.log(arr);

Note that trimming part in the function, is an option you might not need this in your case but I figured out this is what you might want.

You may use _js. Underscore Js Documentation

let fruitsArry = ['apple', 'apple, mango, orange', 'orange'];
var res = _.chain(fruitsArry).map(function(fruit) { return fruit.split(',') }).flatten().value()

console.log(res)