Matching a regex in javascript

Question

I'm trying to extract the date from the following strings but to no avail.

const strs = [
    `X
       March 17th 2011
`,
    `X
       2011
`,
    `X
    March
       2011
`,
];

console.log(strs.map(s => 
  s.match(/X\s+([a-zA-Z]+?\s*[a-zA-Z0-9]+)?\s*(\d+)/))
);

The problem is with the first match, currently it is

[
    "X\n       March 17",
    "March",
    "17"
]

while it should be

[
    "X\n           March 17th 2011",
    "March",
    "17th",
    "2011"
]

Any help would be appreciated.

Welcome to SO! Can the dates change beyond these 3 or is this the entire specification? In other words, are you guaranteed the format full_month_name day_ending_in_th 4_digit_year with the first two fields optional? Or is the logic that X is some sort of hint point and you want to capture anything up to the next 4 digit year after X? — ggorlen
– ggorlen, Commented Sep 29, 2020 at 22:46

Wiktor Stribiżew · Accepted Answer · 2020-09-30 08:25:47Z

1

You can use

/X(?:\s+([a-zA-Z]+))?(?:\s+([a-zA-Z0-9]+))?\s+(\d+)/g

See the regex demo. Details:

X - an X char
(?:\s+([a-zA-Z]+))? - an optional sequence of one or more whitespaces (\s+) and one or more ASCII letters (captured into Group 1)
(?:\s+([a-zA-Z0-9]+))? - an optional sequence of one or more whitespaces (\s+) and one or more ASCII letters or digits (captured into Group 2)
\s+ - 1+ whitespaces
(\d+) - Group 3: one or more digits

See a JavaScript demo below:

const strs = ["X\n           March 17th 2011\n", "X\n           2011\n", "X\n        March\n           2011\n"];
const rx = /X(?:\s+([a-zA-Z]+))?(?:\s+([a-zA-Z0-9]+))?\s+(\d+)/;
strs.forEach(s => 
  console.log( s.match(rx) )
);

Or, getting full values:

const strs = ["X\n           March 17th 2011\n", "X\n           2011\n", "X\n        March\n           2011\n"];
const rx = /X(?:\s+[a-zA-Z]+)?(?:\s+[a-zA-Z0-9]+)?\s+\d+/g;
strs.forEach(s => 
  console.log( s.match(rx).map(x => x.substr(1).trim().replace(/\s+/g, ' ') ))
);

edited Sep 30, 2020 at 8:25

answered Sep 30, 2020 at 8:06

Wiktor Stribiżew

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1 Comment

Wiktor Stribiżew Over a year ago

Just in case: the solution is confirmed to be working. See the demo in the answer, too.

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