Force JS replace to work on all occurrences of needle

When manipulating strings in JavaScript a useful method to know about is the replace() method. It take 2 parameters – the needle and the haystack. So if you wanted to replace ‘cat’ with ‘dog’ it might look something like this:

var myString = "The cat jumped over the fence";
var myNewString = myString.replace("cat","dog");

Great it worked. You can also use regular expressions for the needle if you’re into that kind of thing – say for instance, if you want to generate a valid URL. It when doing just that, that I realised I had a problem on my hands. My code used 2 replace methods – one for removing special characters, the other to remove spaces. The first was a regular expression, while the second was a basic method searching for a space and replacing it with a dash. My problem was that it was only replacing the first space. And so I had to reach for a regular expression to help me out.

Don’t worry if you’re not too great with RegEx, this one is really basic, and here’s what it looks like:

var myString = "The cat jumped over the fence to meet another cat."
var myNewString = myString.replace(/cat+/g,'dog');

That bit of code tells the rendering engine that we are using a RegEx with our forward slashes, inside we have the word we are looking to replace, then the plus symbol tells it to match the preceding word (in our case ‘cat’), 1 or more times. Then the magic happens – we use the ‘g’ character to tell it to look for all occurrences.

And that is how you ensure all occurrences of a needle are replaced when using the replace() method. Hopefully this article will save you scratching your head over why a seemingly obviously method won’t play ball.