JavaScript foreach an array and split them with commas and last one's comma with "and"

Question

I need to know how I can split an array with commas and if it's the last one element to the last one I have , and and if it's the last one I add . to it. I have the following code. The output as one big string honda, audi, tesla, and toyota. the following is printing more than one. Also what if I wanted to push it one time into new array. So one big array of string ["honda, audi, tesla, and toyota."]

let namesArray = ["honda", "audi", "tesla", "toyota"];
let newOrder = ""
namesArray.forEach((item, index) => {
  console.log(index);

  if (index === namesArray.length - 2) {
    newOrder = item + ' , and'
  } else if (index === namesArray.length - 1) {
    newOrder = (item + '.')
  } else {
    newOrder = (item + ',')
  }

})
console.log('new string ', newOrder)

"new string ", "honda,audi,tesla,toyota."

Add "and " and "." to the last element, then use arr.join(", ") — user5734311
– user5734311, Commented May 18, 2021 at 22:42
To fix your existing code you need to append to your existing string, not reassign, so use newOrder += item + .... — Heretic Monkey
– Heretic Monkey, Commented May 18, 2021 at 22:43
@HereticMonkey when i do newOrder.append(item + ' , and') I get Uncaught TypeError: newOrder.append is not a function — Metawaa
– Metawaa, Commented May 18, 2021 at 22:47
... Right. Look at my comment again. I didn't say "use newOrder.append. I said use newOrder += instead of newOrder =. — Heretic Monkey
– Heretic Monkey, Commented May 18, 2021 at 22:49

Nick · Accepted Answer · 2021-05-18 22:47:00Z

4

In terms of what is wrong with your existing code, you are not adding the new string value to your output (i.e. use newOrder +=, not newOrder = in the loop):

let namesArray = ["honda", "audi", "tesla", "toyota"];
let newOrder = ""
namesArray.forEach((item, index) => {
  if (index === namesArray.length - 2) {
    newOrder += item + ', and '
  } else if (index === namesArray.length - 1) {
    newOrder += (item + '.')
  } else {
    newOrder += (item + ', ')
  }

})
console.log(newOrder)

It would be simpler though to just join a slice of the array from the start to the second to last element, then add , and and the last element to that string:

let namesArray=["honda", "audi", "tesla", "toyota"];

let newOrder = namesArray.slice(0,-1).join(', ') + ', and ' + namesArray.slice(-1) + '.';

console.log(newOrder)

edited May 18, 2021 at 22:47

answered May 18, 2021 at 22:41

Nick

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5 Comments

Metawaa Over a year ago

what am I doing wrong. like what if I dont use slice and join. how come my for loop is not doing it

Nick Over a year ago

@blex it will work as long as the array has 2 or more elements, in this case it would produce honda, and audi.

Metawaa Over a year ago

in slice is -1 the last element?

StackSlave Over a year ago

OP should look at that as an index. 0 index starts just before 0.... -1 index is just before the last element. Indexes are always in front of their Array position.

Nick Over a year ago

@Metawaa negative numbers refer to "an offset from the end of the sequence". Since start is inclusive and end is exclusive, slice(-1) includes elements starting from the last element, while slice(0,-1) slices from the first element to the element before the last element.

DecPK · Accepted Answer · 2021-05-18 22:53:28Z

2

You can easily achieve this result using map and join

const arr = ["honda", "audi", "tesla", "toyota"];

const result = arr
  .map((item, index) => {
    if (index === arr.length - 1) {
      return `and ${item}.`;
    } else {
      return `${item}, `;
    }
  })
  .join("");
console.log(result);

You can also use string template literal if the array size in known prior

const arr = ["honda", "audi", "tesla", "toyota"];
const [a, b, c, d] = arr;
const result = `${a}, ${b}, ${c}, and ${d}.`;
console.log(result);

answered May 18, 2021 at 22:53

DecPK

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Comments

StackSlave · Accepted Answer · 2021-05-18 23:01:49Z

0

I would create a function for reuse. First make a .slice() of your array, so the original is not affected. .pop() off the last Array element. Then .join(', ') and concatenate +', and ' along with the element you popped off +'.'.

function andIt(array){
  const a = array.slice(), p = a.pop()+'.';
  if(!a.length){
    return p;
  }
  return a.join(', ')+', and '+p;
}
const namesArray = ['honda', 'audi', 'tesla', 'toyota'];
console.log(andIt(namesArray)); console.log(andIt(['test']));

edited May 18, 2021 at 23:01

answered May 18, 2021 at 22:54

StackSlave

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