Array Methods in JS - join()

Hello guys today i will be discussing join method in javascript.

What is join() used for?
It is used to join the elements of array and returns them as a string
Example -
arr -> ["A","B","C","D"]
After applying join() method on this array
result -> A,B,C,D

Syntax -
array.join(separator)

• separator is the thing which will be applied to all the elements for joining them

Example -

let arr = [1,2,3,4,5]
let joiner = arr.join("-")
console.log(joiner)

Output-

1-2-3-4-5

• As you can see it joins all the elements using the separator "-"

Let's understand this deeply with codes

Example 1 Default join without separator()

const emptyArray = []
const numberArray = [1,2,3,4,5];
const stringArray = ["A","B","C","D"];
const objectArray = [
  {
    name:"Shubham",
    age:21
  },
  {
    name:"Shivam",
    age:25
  },
  {
    name:"Abhishek",
    age:22
  }
]

console.log(emptyArray.join())
console.log(numberArray.join())
console.log(stringArray.join())
console.log(objectArray.join())

Output -

1,2,3,4,5
A,B,C,D
[object Object],[object Object],[object Object]

• As you can see it returns an empty string for empty array
• It joins the array of numbers and strings with comma(,) but for object array it return something different means it can't join array of objects.

Example 2 Join with Separator -

const numberArray1 = [1,2,3,4,5];
const numberArray2 = [6,7,8,9,10];
const stringArray1 = ["A","B","C","D"];
const stringArray2 = ["E","F","G","H"];
const mixedArray = [1,2,3,4,5,"E","F","G","H"]
const exceptionArray = [null,undefined,true,false]


console.log(numberArray1.join("+"))
console.log(numberArray2.join("*"))
console.log(stringArray1.join("["))
console.log(stringArray2.join("z"))
console.log(mixedArray.join("mixed"))
console.log(exceptionArray.join("-"))

Output -

1+2+3+4+5
6*7*8*9*10
A[B[C[D
EzFzGzH
1mixed2mixed3mixed4mixed5mixedEmixedFmixedGmixedH
--true-false

• As you can see we have used different types of separator to join the elements of array.
• Also in exceptionArray you can see that it return empty strings for null and undefined.

Example 3 Applying join on array passed in function parameters

const normalParameter = (arr) => {
  console.log(arr.join("*"))
}

const restParameter = (...args) => {
  console.log(args.join("-"))
}


normalParameter([1,2,3,4,5])
restParameter(1,2,3,4,5)

Output -

1*2*3*4*5
1-2-3-4-5

• It works with arrays passed as function parameters also.

Example 4 Join with other methods -

const arr = [1,2,3,4,5]

// join with reverse
let reverseMethod = arr.reverse().join("")
console.log(reverseMethod)

// join with split method to reverse the array
let splitMethod = arr.join("").split("")
console.log(splitMethod)

Output -

54321
[ '5', '4', '3', '2', '1' ]

• It works with other array and strings method too.

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Also check these posts as well
https://dev.to/shubhamtiwari909/javascript-map-with-filter-2jgo

https://dev.to/shubhamtiwari909/e-quotes-3bng

https://dev.to/shubhamtiwari909/deploy-react-app-on-netlify-kl

Comments

[Andrey Smolko]

I would say that phrase - "join method in javascript" is not a correct one. Method is a function which is combined with an object. Join() is a method of Array.prototype object. So 'Array.prototype.join method in JS' is more correct.

[Shubham Tiwari]

Sure I will change it to that