Using Javascript to merge two standard expressions

Does anyone have a regular expression that can accurately identify the author in these scenarios?

Letter from author to recipient regarding topic 11-10-2018

Letter from author, regarding topic 10-11-2018

I attempted to use the advice provided on this website, and this is what I came up with:

let commaRegex =  new RegExp(/(?<=from) (.+?),/, 'gi','$1');
let fromToRegex = new RegExp(/(?<=from) (.+?) (?=to)/, 'gi','$1');
let combinedRegex = new RegExp(commaRegex + '|' + fromToRegex);
let author = document.getElementById('userInput').value.match(combinedRegex);
console.log(author)

However, when I run console.log(author), it returns 'null'.

I am aware that look behinds are not supported in all browsers, so I am using this code on Chrome. Does anyone have any other suggestions?

javascriptregex

Answer №1

If you want to avoid automatic combination of elements, simply use the or operator for the final part:

(?<=from )(.+?)(?=,| to)

https://regex101.com/r/xzlptd/2/

To ensure compatibility with all browsers, remove the look-arounds from your expression:

from (.+?)(?:,| to)

Then extract the first group from the match using .match(...)[1]

Answer №2

Aside from the solution offered by georg, if you find yourself needing to merge two different things that can't simply be replaced by one:

Rather than including the entire object, you need to add the sources individually:

let commaRegex =  new RegExp(/(?<=from) (.+?),/, 'gi','$1');
let fromToRegex = new RegExp(/(?<=from) (.+?) (?=to)/, 'gi','$1');
let combinedRegex = new RegExp(commaRegex.source + '|' + fromToRegex.source);

let sampleText = 'Letter from Joseph Tribbiani to recipient regarding topic 11-10-2018';

console.log(sampleText.match(combinedRegex));

sampleText = 'Letter from Joseph Tribbiani, regarding topic 11-10-2018';

console.log(sampleText.match(combinedRegex));

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