How to convert an Array to a String in JavaScript

To convert an array to a string in JavaScript you have two methods: toString() and join(). They do the same job, but join() lets you choose the separator.

Using the toString() method on an array will return a string representation of the array:

const list = [1, 2, 3, 4]
list.toString() //'1,2,3,4'

Example:

The join() method of an array returns a concatenation of the array elements:

const list = [1, 2, 3, 4]
list.join() //'1,2,3,4'

Called with no arguments, join() uses a comma, so the result is identical to toString().

The difference is that we can pass a parameter to join() to set a custom separator:

const list = [1, 2, 3, 4]
list.join(', ') //'1, 2, 3, 4'

Example:

This is where join() earns its place. Building a readable list, a path, a CSV line: you pick the separator that fits:

const crumbs = ['home', 'blog', 'javascript']
crumbs.join(' / ') //'home / blog / javascript'

A few edge cases

An empty array gives you an empty string:

[].join() //''

null and undefined elements become empty strings, so they leave gaps between separators:

[1, null, undefined, 4].join('-') //'1---4'

Nested arrays get converted too, with their own commas, which can produce confusing output:

[1, [2, 3], 4].join('-') //'1-2,3-4'

Watch out for objects

Be careful when the array contains objects. Both methods convert each element by calling its own toString(), and for a plain object that returns the famous useless string:

const users = [{ name: 'Flavio' }]
users.toString() //'[object Object]'

If your goal is to serialize data, not display it, join() is the wrong tool. Use JSON.stringify() instead:

JSON.stringify([{ name: 'Flavio' }]) //'[{"name":"Flavio"}]'

My rule of thumb: join() for strings and numbers you want to show to a human, JSON.stringify() for data you want to store or send.