How To Manipulate Strings in JavaScript

Combine and repeat strings, change cases, remove whitespace, and more

Photo by John Hult on Unsplash

JavaScript has built-in functions and constructs to do most string operations. The ones that don’t can be done with a few simple function calls.

Combine Strings

Concatenation

There are two ways to do it. One way is to use the concat function.

For example:

const hello = "Hello ";
const bob = "Bob!";
const res = hello.concat(bob); // Hello Bob!

Another way is to use the + operator, like so:

const hello = "Hello ";
const bob = "Bob!";
const res = hello + bob; // Hello Bob!

Template strings

ES6 or later has template strings so you can include strings within another string, like this:

const hello = "Hello ";
const bob = "Bob!";
const res = `${hello} ${bob}`; // Hello Bob!

Array.join

If you have an array of strings, you can combine the entries with the same separator between them, with the join function, like this:

const arr = ['Hello', 'Bob'];
const res = arr.join(' '); // 'Hello Bob'

Get Substring

String.substr

JavaScript strings have a substr function to get the substring of a string.

It takes a starting index as the first argument and a number of characters from the start index, and so on as the second argument.

It can be used like this:

const str = "Hello Bob";
const res = str.substr(1, 4); // ello

String.substring

JavaScript strings also have a substring function that takes the start and end index as two arguments and returns a string with the ones between the start and end indices.

The start index is included but the end index is excluded.

Example:

const str = "Hello Bob";
const res = str.substring(1, 3); // el

Changing Cases