Javascript Replace with Regex Match Not Working

Question

I'm trying to truncate some longitude coordinates without any rounding issues. I thought replace() would be the simplest way to do this.

My regex is correct, but I'm apparently not using replace correctly.

Here's my stripped down example. I need to strip all decimal points after the 8th position

var truncRegex = /-?\d+?\.\d{8}/;
console.log('-81.82297519999997'.replace(truncRegex, '$1'));

What's happening is replace() is stripping the match and leaving me with the remainder prepended with "$1". The result is: $1999997

If you aren't concerned about rounding, you could use Number("...").toFixed(8) — chazsolo
– chazsolo, Commented Dec 11, 2014 at 23:39

Leo · Accepted Answer · 2014-12-12 04:56:38Z

1

You've got some answers of RegExp. Alternatively, you could just find the index of the point and retrieve a substring, if you don't care about rounding.

var str = '-81.82297519999997';
var truncated = str.substring(0, str.indexOf('.') + 9); // this will give you 8 fractions
console.log(truncated); // "-81.82297519"

answered Dec 12, 2014 at 4:56

Leo

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Brandon Buster Over a year ago

This was my fix. Thank you.

Andrew Dunai · Accepted Answer · 2014-12-11 23:43:14Z

0

You must add matching groups in parentheses to match something that you can refer to with $1 while replacing. For example:

var truncRegex = /(-?\d+?\.\d{8})\d*/;
console.log('-81.82297519999997'.replace(truncRegex, '$1'));

replace() function replaces everything it matches based on regular expression. Your code simply replaces -DD.DDDDDDDD with '$1' string.

You can still use expression you provided, but you will have to use match, not replace, e.g.:

var truncRegex = /-?\d+?\.\d{8}/;
console.log('-81.82297519999997'.match(truncRegex)[0]);

answered Dec 11, 2014 at 23:43

Andrew Dunai

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hoipolloi · Accepted Answer · 2014-12-11 23:48:00Z

0

var s = '81.82297519999997';

// Returns "-81.82297519"
s.replace(/(-?\d+\.\d{8})\d*/, '$1');

answered Dec 11, 2014 at 23:48

hoipolloi

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vks · Accepted Answer · 2014-12-12 04:44:27Z

0

(-?\d+?\.\d{8})|.*

Try this.Replace by $1.See demo.

https://regex101.com/r/eZ0yP4/17

var re = /(-?\d+?\.\d{8})|.*/mg;
var str = '-81.82297519999997';
var subst = '$1';

var result = str.replace(re, subst);

answered Dec 12, 2014 at 4:44

vks

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