I need to detect currency and extract digit from such strings as "10 dollars", "dollars 10", etc. I use String.prototype.match() and regex
/((dollar|usd\$)\s*(\d+)|(\d+)\s*(dollar|usd\$))/i
But match() returns me for "10 dollars"
["10 dollar", "10 dollar", undefined, undefined, "10", "dollar"]
and for "dollar 10"
["dollar 10", "dollar 10", "dollar", "10", undefined, undefined]
How I can avoid that situation and get predictable digit position ?
You may check which group matched and then grab the necessary value.
I suggest simplifying the structure a bit by turning alternations to non-capturing groups and removing the outer group:
/(?:dollars?|usd\$)\s*(\d+)|(\d+)\s*(?:dollars?|usd\$)/i
See this demo
A demo test:
var re = /(?:dollars?|usd\$)\s*(\d+)|(\d+)\s*(?:dollars?|usd\$)/i;
var strs = ["10 dollars", "dollars 30"];
for(var t of strs) {
var m = t.match(re);
if (m && m[2])
console.log(m[2]);
else if (m) console.log(m[1]);
}You can mark any group (things in (parentheses)) in a regex as "non-capturing" by adding ?: after the left paren, as in (?:non|capturing|group).
So if all you want is the digits, not the word "dollar" or "usd", you could do:
/(?:(?:dollar|usd\$)\s*(\d+)|(\d+)\s*(?:dollar|usd\$))/i
That will give you ["dollar 10", undefined, "10"] for "10 dollars". From there, just do:
var matches = myString.match(/(?:(?:dollar|usd\$)\s*(\d+)|(\d+)\s*(?:dollar|usd\$))/i);
var amount = matches[2] || matches[1];
/(\d+)\ (dollar|usd)|(dollar|usd)\ (\d+)/gi