How do you access the matched groups in a JavaScri

Question

I want to match a portion of a string using a regular expression and then access that parenthesized substring:

var myString = "something format_abc"; // I want "abc"

var arr = /(?:^|\s)format_(.*?)(?:\s|$)/.exec(myString);

console.log(arr);     // Prints: [" format_abc", "abc"] .. so far so good.
console.log(arr[1]);  // Prints: undefined  (???)
console.log(arr[0]);  // Prints: format_undefined (!!!)

What am I doing wrong?

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I've discovered that there was nothing wrong with the regular expression code above: the actual string which I was testing against was this:

"date format_%A"

Reporting that "%A" is undefined seems a very strange behaviour, but it is not directly related to this question, so I've opened a new one, Why is a matched substring returning "undefined" in JavaScript?.

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The issue was that console.log takes its parameters like a printf statement, and since the string I was logging ("%A") had a special value, it was trying to find the value of the next parameter.

Answer 1

Last but not least, I found one line of code that worked fine for me (JS ES6):

let reg = /#([\S]+)/igm; // Get hashtags.
let string = 'mi alegría es total! ✌                                                                    

                                                        
            

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