JavaScript Regex: Positive Lookbehind Alternative (For Safari and Other Browsers That Do Not Support Lookbehinds)

JavaScript regex: Positive lookbehind alternative (for Safari and other browsers that do not support lookbehinds)

Turn the lookbehind in a consuming pattern and use a capturing group:

And use it as shown below:

var s = "some string.005";
var rx = /\.\d\d(\d)/;
var m = s.match(/\.\d\d(\d)/);
if (m) {
  console.log(m[1]);
}

javascript regex - look behind alternative?

^(?!filename).+\.js works for me

tested against:

• test.js match
• blabla.js match
• filename.js no match

A proper explanation for this regex can be found at Regular expression to match string not containing a word?

Look ahead is available since version 1.5 of javascript and is supported by all major browsers

Updated to match filename2.js and 2filename.js but not filename.js

(^(?!filename\.js$).).+\.js

Regex positive lookbehind alternative for word wrap

Use

return text.replace(/(.{45})(?!$)/g, "$1\r\n");

See regex proof.

EXPLANATION

NODE                     EXPLANATION
--------------------------------------------------------------------------------
  (                        group and capture to \1:
--------------------------------------------------------------------------------
    .{45}                    any character except \n (45 times)
--------------------------------------------------------------------------------
  )                        end of \1
--------------------------------------------------------------------------------
  (?!                      look ahead to see if there is not:
--------------------------------------------------------------------------------
    $                        before an optional \n, and the end of
                             the string
--------------------------------------------------------------------------------
  )                        end of look-ahead

JS Regex lookbehind not working in firefox and safari

Firefox and ^Has

Safari doesn't have support for lookbehind yet, you can use capture group ( used so that this the pattern on which we are splitting will be also be added in output ) and split on <tag> </tag>

let str = "The quick brown <tag>fox</tag> jumps over the lazy <tag>dog</tag>"

let regex = /(<tag>.*?<\/tag>)/

console.log(str.split(regex).filter(Boolean))

Regex lookbehind alternative for Safari

I doubt there is a way with a single regex with no lookbehind or conditionals support thus I suggest the following approach combining regex and additional programming logic:

var texts = ['abcfobar','abc33bar'];
var regex = /^([a-zA-Z0-9]{0,3})(?:([a-zA-Z]{1,2})([a-zA-Z0-9]+)?)?/;
for (var i=0; i<texts.length;i++) {
  var serialCode = '';
  var serialMarket = '';
  var serialSuffixmatch = ''; 
  var match = texts[i].match(regex);
  if (match) {
    serialCode = match[1];
    serialMarket = (match[2] || "");
    if (serialCode.length == 3 && serialMarket.length == 2) {
      serialSuffixmatch = match[3];
    }
  }
  console.log(texts[i], '=>', serialCode + "\n" + serialMarket + "\n" + serialSuffixmatch);
}

JavaScript regex: Positive lookbehind alternative (for Safari and other browsers that do not support lookbehinds)

Turn the lookbehind in a consuming pattern and use a capturing group:

And use it as shown below:

var s = "some string.005";
var rx = /\.\d\d(\d)/;
var m = s.match(/\.\d\d(\d)/);
if (m) {
  console.log(m[1]);
}

JavaScript support of Lookaheads and Lookbehinds in Regular Expressions

Javascript has support for only positive and negative lookahead with no support whatsoever for lookbehinds, but you can still mimic the latter in Javascript using callbacks.

There is a nice article about this here, actually although this article uses callbacks to provide some sort of an alternative support for lookbehind, the same principle can be used in other languages that support lookbehinds but not variable expressions in them so it is handy trick.

Alternative to positive lookbehind regex

If you can only provide a regex and the whole match value is highlighted, there is no way to mimic the current lookbehind pattern. The best you could think of is a regex like
/\b\s(\w+)(?=\s\w)/ that would also highlight the leading whitespace (unless there is an option to highlight only some group value).

If you can tweak the inner code, you could use a group replacement: find /(\w\s)(\w+)(?=\s\w)/ and replace with $1<span class="highlight">$2</span>.

Trying to find regex lookbehind alternative for GAS

v[r][0] = v[r][0].replace(/^(.{5})(:00)/, "$1");

This breaks the regular expression into two capture groups, and the "$1" just returns the first group.

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