What are these regex supposed to do?

Posted on 2013-11-26
Last Modified: 2013-12-11
The html includes a span tag with id="productPrice" which wraps around a price with currency symbol, and the in-page javascript includes a variable called baseprice which is set to be the innerHTML of productPrice and therefore includes the currency symbol.

Can you tell me please what does the regex do in the following code?
document.getElementById('productPrice').innerHTML = baseprice.replace(/[+-]*(d+).(d+)/, total.toFixed(2));

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The next alternative code is an extended version of the one above; Can you tell me please what does the next regex do?
document.getElementById('productPrice').innerHTML = baseprice.replace(/[+-]*(d+).(d+)/, total.toFixed(2).replace(/(d)(?=(d{3})+.)/g, "$1,"));

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The code above does not seem to work, the following does except that it loses the currency symbol:
document.getElementById('productPrice').innerHTML = total.toFixed(2);

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Question by:ncw
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Accepted Solution

Derek Jensen earned 500 total points
ID: 39678281
baseprice.replace(/[+-]*(d+).(d+)/, total.toFixed(2));

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Okay so what's happening here is within the baseprice var it is:
[+-]*    // Looking for any plus or minus symbols (or possibly both or neither)
(d+)     // then, looking for at least one consecutive digits (and storing it in capture group $1)
.          // then it's looking for any single char (I'm thinking they meant to put \. to look specifically for a period char)
(d+)     // and finally it's looking for another consecutive string of at least one digit (stored in $2)
, total.toFixed(2)    // And, upon finding a match, replacing the entire matched group with total.toFixed(2) -- which also renders the capture groups unnecessary.

baseprice.replace(/[+-]*(d+).(d+)/, total.toFixed(2).replace(/(d)(?=(d{3})+.)/g, "$1,"));

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What's happening here is...well no wonder it's not working...

Okay so what the designer was *trying* to accomplish is to find any three consecutive digits and place a comma after it. The only way I was able to accomplish this correctly using regexes was by using two of them, as demonstrated here, although I'm convinced there's an easier way to do it.

There is no regex replace happening here, so of course it would not be inserting any commas :-)
document.getElementById('productPrice').innerHTML = total.toFixed(2);

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Expert Comment

ID: 39680335
I suggest you to take a look to W3 schools tutorials ( and Th ToFixed JS function converts a number to a string, keeping the number of decimals you want (see

Expert Comment

by:Derek Jensen
ID: 39681026
@ncw wasn't asking what .toFixed() did, he asked what the regexes did, so I explained it. total.toFixed(2) was in the replace argv of .replace(). :-)

Author Closing Comment

ID: 39711686
Many thanks!

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