Regex checking lat/lon in JavaScript

Question

I'm such a newb in regex, but still...
I based my test on this post.

I have this simple regex :

^-?([1]?[1-7][1-9]|[1]?[1-8][0]|[1-9]?[0-9])\.{1}\d{1,6}

In Debuggex, if I test it with 88.5 for example, it matches.

In my JS file, I have :

var lonRegex = new RegExp("^-?([1-8]?[1-9]|[1-9]0)\.{1}\d{1,6}");
var check = lonRegex.test(88.5); // hardcoded for demo
console.log(check) // output false

I can't guess why it's always returning me false, whatever the value is a number or a string like "88.5".

This has something to do with how regex parts are escaped when creating a regex object from a string. /^-?([1-8]?[1-9]|[1-9]0)\.{1}\d{1,6}/.test(88.5) will return true — lxe
– lxe, Commented Nov 6, 2014 at 23:34
Don't construct a regexp from a string, just use a regex literal (/.../). Also, don't check numbers with a regexp, just check them with arithmetic. — user663031
– user663031, Commented Nov 7, 2014 at 3:46

lxe · Accepted Answer · 2014-11-06 23:39:52Z

1

You will need to escape some characters when creating a RegExp object from a string. From MDN:

When using the constructor function, the normal string escape rules (preceding special characters with \ when included in a string) are necessary.

In your case, this will work (note the double \ for \d and .):

var lonRegex = new RegExp("^-?([1-8]?[1-9]|[1-9]0)\\.{1}\\d{1,6}");
var check = lonRegex.test(88.5); // hardcoded for demo
console.log(check) // output true

answered Nov 6, 2014 at 23:39

lxe

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2 Comments

David Knipe Over a year ago

Equivalently, you could use var lonRegex = /^-?([1-8]?[1-9]|[1-9]0)\.{1}\d{1,6}/;.

David Knipe Over a year ago

Also, it gives the wrong results for (for example) 0.5 and 90.5.

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