Converting Ruby regex expression to JavaScript

Question

I am working on a text justify function in JavaScript and i'd like to use a regex snippet that worked for my previous Ruby justify function.

The regex is as follows:

/(?<=\s|\A).{1,#{length}}(?=\s|\z)/

I'm using this as a template to extract a line of text that's within a specified length variable from a larger string that doesn't have line-returns. The regex ensures that I am capturing all complete words and requisite whitespace within this length and not cutting any words off.

I'd like to create a JavaScript analogue of this regex.

I've tried the basic replace of syntax between Ruby and JS, as follows:

^\s|\A.{1,length}\s|\z$

with no success. Any help would be greatly appreciated.

github.com/VerbalExpressions/JSVerbalExpressions might be useful — Ismael
– Ismael, Commented Jan 20, 2016 at 23:17
Lookbehind is not supported and you got it right that you removed it. Now, the anchors \A and \z are not supported either. You will need to use a constructor notation to declare a dynamic pattern as variable interpolation does not work as in Ruby. Use something like var length = 5; var rx = RegExp("(?:\\s|^)(.{1, " + length + "})(?=\\s|$)", "g"); - your value will be in Group 1 (you will need to run RegExp#exec in a while loop). — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Jan 20, 2016 at 23:19

Wiktor Stribiżew · Accepted Answer · 2016-01-20 23:48:29Z

1

Lookbehind is not supported and you got it right that you removed it. Now, the anchors \A and \z are not supported either. You will need to use a constructor notation to declare a dynamic pattern as variable interpolation does not work as in Ruby.

Use something like

var length = 5; 
var re = RegExp("(?:\\s|^)(.{1," + length + "})(?=\\s|$)", "g");
var str = 'My cool code on StackOverflow.';
var res = [];
while ((m = re.exec(str)) !== null) {
  res.push(m[1]);            // Your value is in Group 1
}
document.body.innerHTML = "<pre>" + JSON.stringify(res, 0, 4) + "</pre>"; // just demo

answered Jan 20, 2016 at 23:48

Wiktor Stribiżew

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