Reverse String in Javascript

Published on 06 May 2018 (Updated: 15 May 2023)

Welcome to the Reverse String in Javascript page! Here, you'll find the source code for this program as well as a description of how the program works.

Current Solution

const reverse = s => s.split('').reverse().join('');

if (process.argv.length > 2) {

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How to Implement the Solution

Let's look at the code in detail.

const reverse = s => s.split('').reverse().join('');

First there is a function declaration reverse which takes one parameter s. The reverse function returns a method chain of the s parameter. It assumes that the parameter is of type string. A string in JavaScript offers numerous methods, like .toLowerCase(), which would mutate a string to all lowercase letters.

Another method of the String object is the split method which you can see above. split() takes two optional parameters, a seperator and a limit. In the reverse function it is used with an empty string '' as a seperator. This has the effect of splitting the string at every character. The return value of the split method is, and this makes the beauty of this solution, an array, which has it's own methods built in.

If you call the reverse function above, for example with 'hello', the split method would return ['h', 'e', 'l', 'l', 'o']. Since this is an array you can immediately use one of the various array methods available in JavaScript. Luckily the language helps us a lot here, since it already has a method .reverse() to reverse an array.

Now we are at the second chained method and our hypothetical output would look like this ['o', 'l', 'l', 'e', 'h']. We are just one step ahead of our solution.

All we need to do now is to somehow get back to a string. One of the array methods JavaScript offers us is the .join() method. It, kind of, is the opposite of the split method as it brings an array back together, based on an optional seperator parameter, and returns a string. Like the split method an empty string as a parameter means that it will execute on every value in the array. Since we have single characters as values it will simply concatenate them together to our string.

Now, let's look at the rest of the code:

if (process.argv.length > 2) {

process.argv contains the command-line arguments. We make sure there are enough. If so, we call our reverse function with the first one (process.argv[2], since the first two, process.argv[0] and process.argv[1] can be ignored). Then, console.log displays the reversed string returned from the reverse method.

Now our solution is complete.

How to Run the Solution

To run this example you can simply open the dev tools of your browser (F12) in most cases and navigate to the console tab. There you can paste in the code snippet from above.

Alternatively you can paste the code into an online Javascript interpreter.