Javascript: wrap matched regex with tags

Question

I am trying to surround dates in middleRsults with tags:

var middleRsults = "95.00      04/07/15    aaaa  10/02/15 ";
var regex =/\d{2}\/\d{2}\/\d{2}/g;
var x= middleRsults.replace(regex,"<b>$1</b>")

What I want to get:

  95.00      <b>04/07/15</b>    aaaa  <b>10/02/15</b>

instead, what I actually get:

95.00      <b>$1</b>    aaaa  <b>$1</b>

I search a lot, but couldn't figure out why this is happening with this specific regex that I am using.

Read the documentation carefully to learn what $1 means, and what other special replacement patterns are available. — user663031
– user663031, Commented Dec 25, 2016 at 16:17

Yosvel Quintero · Accepted Answer · 2016-12-25 15:19:24Z

3

With your current regular expression you can simply use the matched substring $&:

var middleRsults = '95.00      04/07/15    aaaa  10/02/15 ',
    regex = /\d{2}\/\d{2}\/\d{2}/g,
    x = middleRsults.replace(regex, '<b>$&</b>');

console.log(x);

Or, for more complex situations, you can specify a function as a parameter where match is the matched substring (Corresponds to $& above.):

var middleRsults = '95.00      04/07/15    aaaa  10/02/15 ',
    regex = /\d{2}\/\d{2}\/\d{2}/g,
    x = middleRsults.replace(regex, match => `<b>${match}</b>`);

console.log(x);

edited Dec 25, 2016 at 15:19

answered Dec 25, 2016 at 15:03

Yosvel Quintero

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Pointy · Accepted Answer · 2016-12-25 14:58:39Z

1

You need a capturing group to use the $n replacement:

var regex =/(\d{2}\/\d{2}\/\d{2})/g;

The parentheses form such a group. The groups are numbered left-to-right in the pattern.

answered Dec 25, 2016 at 14:58

Pointy

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elldur · Accepted Answer · 2016-12-25 14:58:54Z

1

You'll probably face-palm when you realise this but your regex doesn't contain a capture group for $1 to refer to.

This should hopefully fix it:

var regex = /(\d{2}\/\d{2}\/\d{2})/g;

answered Dec 25, 2016 at 14:58

elldur

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