I want to create a JS function that adds a string ending to each member in an array. The expected function when called should return something like this:

addEnding(["clever", "meek", "hurried", "nice"], "ly")

Expected output:

["cleverly", "meekly", "hurriedly", "nicely"] 

Thanks for all answers suggesting to use map method, but I want to use a for loop, here is what my code looks like:

const addEnding = (arr, str) => {
  let result = '';
  for (i = 0; i < arr.length; i++) {
    result = arr[i]
    result += str
  }
  return result
}

console.log(addEnding(["new", "pander", "scoop"], "er"))

I want to create a JS function that adds a string ending to each member in an array. The expected function when called should return something like this:

addEnding(["clever", "meek", "hurried", "nice"], "ly")

Expected output:

["cleverly", "meekly", "hurriedly", "nicely"] 

Thanks for all answers suggesting to use map method, but I want to use a for loop, here is what my code looks like:

const addEnding = (arr, str) => {
  let result = '';
  for (i = 0; i < arr.length; i++) {
    result = arr[i]
    result += str
  }
  return result
}

console.log(addEnding(["new", "pander", "scoop"], "er"))

The issue is that it only returns the first element of an array, when I expect it to return all elements from array + str ending

• javascript
• arrays
• string

• Using map() method returns a new array, it does not modify the existing one. It is better to use for/forEach loops if you are looking to update the exisiting array. Check my answer as well. – hygull Commented Apr 3, 2019 at 4:30
• In your case the little mistake you did is, you used result variable and updated that. Use arr[i] = arr[i] + str. – hygull Commented Apr 3, 2019 at 4:33

10 Answers 10

You declared the result as a string and replace it over the iteration. Just change the data type to array as you expected.

const addEnding = (arr, str) => { 
  let result = '' // You initiated a string as a result not an array
  for(i=0; i<arr.length; i++) {
    result = arr[i]  // The string got replaced every time it interate
    result += str 
  } 
  return result // The result is always the last item
} 
console.log(addEnding(["new", "pander", "scoop"], "er"))

const arr =["new", "pander", "scoop"]
const str = 'er'

const addEnding = (arr, str) => { 
  let result = []; // Init an array as format output
  for(i=0; i<arr.length; i++) {
    result[i] = arr[i] + str  // assign like this
  } 
  return result 
} 
console.log(addEnding(arr, str))

use map function, which will iterate over your array and return a new array with the modified version of each.

Using string interpolation you can append easily the suffix

function addEnding(arr, end) {
  return arr.map(word => `${word}${end}`);
}

console.log(addEnding(["clever", "meek", "hurried", "nice"], "ly"))

function addSuffix(arr, suff){
    var newArr=[];
    for (var i = 0; i < arr.length; i++)
       newArr.push(arr[i] + suff);

    return newArr;

}

Try to the following code

function addEnding(array, suffix) {

  if (Array.isArray(array)) {
    for (var i = 0; i < array.length; i++) {
      array[i] = array[i] + suffix;
    }
  }
  return array;
}

console.log(addEnding(["clever", "meek", "hurried", "nice"], "ly"));

You can use Array#map along with String#concat

function addEnding(words, suffix) {
  return words.map(word => word.concat(suffix))
}

const output = addEnding(["clever", "meek", "hurried", "nice"], "ly");
console.log(output);

If you are looking to use for loop and want to do this in a functional way (the way you choose) then you can try like this.

I have executed the statements on Node REPL.

Note » Using map() method returns a new array, it does not modify the existing one. It is better to use for/forEach loops if you are looking to update the exisiting array.

Your mistake: In your case the little mistake you did is » you used result variable and updated that. Use arr[i] = arr[i] + str.

> const addEnding = (arr, str) => {
... arr.forEach((item, i) => {
.....     arr[i] = item + str;
..... })
... return arr
... }
undefined
> 
> addEnding(["clever", "meek", "hurried", "nice"], "ly")
[ 'cleverly', 'meekly', 'hurriedly', 'nicely' ]
> 
> addEnding(["new", "pander", "scoop"], "er")
[ 'newer', 'panderer', 'scooper' ]
> 

function wordConverter(arr, str) {
    return arr.map(x => x.concat(str));
}

console.log(wordConverter(['clean', 'dye', 'dry', 'call'], 'ing'));

Use map which will return a new array of words formed by concatenating words from original array and the suffix

function addEnding(array, suffix) {
  // assuring input is array otherwise map will not work
  if (Array.isArray(array)) {
    return array.map(item => item + suffix)
  }
}
   console.log(addEnding(["clever", "meek", "hurried", "nice"], "ly"))

Use Array.prototype.map()

const addEnding = (array, suffix) => array.map(word => `${word}${suffix}`);
const result = addEnding(["clever", "meek", "hurried", "nice"], "ly");

console.log(result);

You can do it with the below function if you want to use the traditional for loop.

function addEnding(arr, end) {
  for(let i=0; i<= arr.length-1; i++)
      arr[i] += end;
  return arr;
}