I wanted to write a regex to count the number of spaces/tabs/newline in a chunk of text. So I naively wrote the following:-
numSpaces : function(text) {
return text.match(/\s/).length;
}
For some unknown reasons it always returns 1
. What is the problem with the above statement? I have since solved the problem with the following:-
numSpaces : function(text) {
return (text.split(/\s/).length -1);
}
This question is related to
javascript
regex
This is certainly something that has a lot of traps. I was working with Paolo Bergantino's answer, and realising that even that has some limitations. I found working with string representations of dates a good place to quickly find some of the main problems. Start with an input string like this:
'12-2-2019 5:1:48.670'
and set up Paolo's function like this:
function count(re, str) {
if (typeof re !== "string") {
return 0;
}
re = (re === '.') ? ('\\' + re) : re;
var cre = new RegExp(re, 'g');
return ((str || '').match(cre) || []).length;
}
I wanted the regular expression to be passed in, so that the function is more reusable, secondly, I wanted the parameter to be a string, so that the client doesn't have to make the regex, but simply match on the string, like a standard string utility class method.
Now, here you can see that I'm dealing with issues with the input. With the following:
if (typeof re !== "string") {
return 0;
}
I am ensuring that the input isn't anything like the literal 0
, false
, undefined
, or null
, none of which are strings. Since these literals are not in the input string, there should be no matches, but it should match '0'
, which is a string.
With the following:
re = (re === '.') ? ('\\' + re) : re;
I am dealing with the fact that the RegExp constructor will (I think, wrongly) interpret the string '.'
as the all character matcher \.\
Finally, because I am using the RegExp constructor, I need to give it the global 'g'
flag so that it counts all matches, not just the first one, similar to the suggestions in other posts.
I realise that this is an extremely late answer, but it might be helpful to someone stumbling along here. BTW here's the TypeScript version:
function count(re: string, str: string): number {
if (typeof re !== 'string') {
return 0;
}
re = (re === '.') ? ('\\' + re) : re;
const cre = new RegExp(re, 'g');
return ((str || '').match(cre) || []).length;
}
(('a a a').match(/b/g) || []).length; // 0
(('a a a').match(/a/g) || []).length; // 3
Based on https://stackoverflow.com/a/48195124/16777 but fixed to actually work in zero-results case.
('my string'.match(/\s/g) || []).length;
As mentioned in my earlier answer, you can use RegExp.exec()
to iterate over all matches and count each occurrence; the advantage is limited to memory only, because on the whole it's about 20% slower than using String.match()
.
var re = /\s/g,
count = 0;
while (re.exec(text) !== null) {
++count;
}
return count;
how about like this
function isint(str){
if(str.match(/\d/g).length==str.length){
return true;
}
else {
return false
}
}
Source: Stackoverflow.com