React-Native: JavaScript regular expression exception (Invalid group) on release mode

Question

I wrote following function in order to parse available image sizes inside srcset attribute for each img element and return it as array. Everything works as expected when the debug mode is on, but once I disable the debug mode, the app would crash and throw following error:

Error: invalid regular expression invalid group specifier name

export function srcsetParser(htmlString) {

  let result = [];
  let images = htmlString.match(/<img\s+[^>]*srcset="([^"]*)"[^>]*>/g); // Finding img tags inside html string

  images && images.forEach(image => {
    let srcsets = image.match(/(?<=srcset=").+?(?=\")/g); //Select srcset value

    var urls = srcsets[0].split(", ");
    urls.forEach(url => {
      let temp = url.split(" ");
      result.push(temp[0]);
    });
  });
  return result;
}

Any idea what's wrong with the regex and why is it so only when debug mode is off ?

Thanks

Anonymous · Accepted Answer · 2019-01-20 20:02:19Z

1

Update

The browser support isn’t great, but JavaScript now allows lookbehinds. The old answer is left below.

JavaScript regex doesn’t support lookbehinds. You can do it another way:

  images && images.forEach(image => {
    let srcsets = image.match(/srcset="(.+?)(?=\")/); //Select srcset value

    var urls = srcsets[1].split(", ");
    urls.forEach(url => {
      let temp = url.split(" ");
      result.push(temp[0]);
    });
  });

edited Jan 20, 2019 at 20:02

answered Jul 16, 2018 at 23:01

Anonymous

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7 Comments

Ehsan Ahmadizadeh Over a year ago

but /srcset="(.+?)(?=\")/g would include srcset=, is there a way to avoid that ?

Anonymous Over a year ago

@EhsanAhmadizadeh I also changed srcsets[0] to srcsets[1]. srcset= should not be included.

Ehsan Ahmadizadeh Over a year ago

But srcsets[1] is undefined for me!

Anonymous Over a year ago

@EhsanAhmadizadeh Sorry, you have to also remove the g flag. Updated.

Ehsan Ahmadizadeh Over a year ago

That did it. Thanks but why does it return two results instead of one ? There's no way with regex to just extract the text after srcset=" till the next occurrence of " ?

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