Javascript regex escape dot following digits

Question

I would like to test a string which should start with any number of digits but not followed by a dot, so I come up these regs, code in jsfiddle:

var startwith = "some string";
    reg1 = new RegExp("^" + startWith + "[0-9]+(?!\\.)"),
    reg2 = new RegExp("^" + startWith + "\d+(?!\\.)");

var text = "11.1";

console.log(reg1.test(text), reg2.test(text)); // result true, false

I started with reg1, but it fails to return the correct result, so I was just trying the reg2. Surprisingly, the result is correct, but what confuses me is that the two regs return different result, while the patterns are basically equivalent. Anybody have any ideas? all thoughts are appreciated.

does this work for a replacement for reg1? new RegExp("^(0-9)+(?!\\.)") — J Carroll
– J Carroll, Commented Jul 4, 2014 at 19:53
Why are you writing \\., but just \d? What is the difference? — Kobi
– Kobi, Commented Jul 4, 2014 at 19:55
@kobi, good question, but with single backslash won't work for some reason, which I don't know. — bingjie2680
– bingjie2680, Commented Jul 4, 2014 at 20:00
RegExp constructor requires double slash so \\d instead of \d and \\. instead of \. since it accepts a string in constructor. One backslash is for Javascript string and 2nd one is for Javascript regex engine. — anubhava
– anubhava, Commented Jul 4, 2014 at 20:03

Community · Accepted Answer · 2020-06-20 09:12:55Z

1

This should work:

var re = /^\d+(?!\.)\b/;

Problem is that in your regex without word boundary regex matches only first 1 of 11.1 and since next one is not a dot it returns true. You need to force it match till a word boundary is reached.

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edited Jun 20, 2020 at 9:12

CommunityBot

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answered Jul 4, 2014 at 19:55

anubhava

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bingjie2680 Over a year ago

looks promising. will try it.

zx81 · Accepted Answer · 2014-07-04 19:57:20Z

0

Start with any digit not followed by a dot:

if (/^\d(?!\.)/.test(yourString)) {
    // It matches!
} else {
    // Nah, no match...
}

answered Jul 4, 2014 at 19:57

zx81

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1 Comment

bingjie2680 Over a year ago

sorry, not only single digits, but multiple digits.

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