How to join two strings in JavaScript

To join two strings in JavaScript you use the + operator. There are a couple of alternatives too, and we’ll look at all of them.

If you have a string name and a string surname, you can assign them to the fullname variable like this:

const name = 'Flavio'
const surname = 'Copes'

const fullname = name + surname

console.log(fullname) // 'FlavioCopes'

Notice the two words are glued together. + does not add any separator, so if you want a space in between you concatenate one yourself:

const fullname = name + ' ' + surname

console.log(fullname) // 'Flavio Copes'

If you don’t want to instantiate a new variable, you can use the += operator to add the second string to the first:

let name = 'Flavio'
name += ' Copes'

Notice that name is declared with let here. += reassigns the variable, so if name was a const you’d get TypeError: Assignment to constant variable.

Alternatively you can also use the concat() method of the String object, which returns a new string concatenating the one you call this method on, with the argument of the method:

const fullname = name.concat(surname)

When you’re joining strings with other text around them, a template literal is often the cleanest option:

const greeting = `Hello ${name} ${surname}!`

console.log(greeting) // 'Hello Flavio Copes!'

And if you have more than two strings, you can put them in an array and call join() with the separator you want:

const parts = ['Flavio', 'Copes']

console.log(parts.join(' ')) // 'Flavio Copes'

Watch out for numbers

One thing that trips people up: + also does addition. If one of the two operands is a string, JavaScript converts the other to a string and concatenates:

const price = 10
const label = price + '2'

console.log(label) // '102'

You expected 12, you got the string '102'. If a value might be a number, convert it explicitly with String() (or the number with Number()) so the intent is clear.

I generally recommend the simplest route, which is using the + (or +=) operator, and template literals when you’re building a longer string out of several pieces.