CODEWITHSUNDEEP
javascriptregexregex-lookaroundssplitlookbehind
hippietrail
hippietrail

Reputation: 17023

Split string in JavaScript using regex with zero width lookbehind

I know JavaScript regular expressions have native lookaheads but not lookbehinds.

I want to split a string at points either beginning with any member of one set of characters or ending with any member of another set of characters.

Split before ເ, ແ, ໂ, ໃ, ໄ. Split after ະ.

In: ເລື້ອຍໆມະຫັດສະຈັນເອກອັກຄະລັດຖະທູດ

Out: ເລື້ອຍໆມະ ຫັດສະ ຈັນ ເອກອັກຄະ ລັດຖະ ທູດ

I can achieve the "split before" part using zero-width lookahead:

'ເລື້ອຍໆມະຫັດສະຈັນເອກອັກຄະລັດຖະທູດ'.split(/(?=[ໃໄໂເແ])/)

["ເລື້ອຍໆມະຫັດສະຈັນ", "ເອກອັກຄະລັດຖະທູດ"]

But I can't think of a general approach to simulating zero-width lookbehind

I'm splitting strings of arbitrary Unicode text so don't want to substitute in special markers in a first pass, since I can't guarantee the absence of any string from my input.

Upvotes: 1

Views: 364

Answers (3)

hwnd
hwnd

Reputation: 70750

Instead of spliting, you may consider using the match() method.

var s = 'ເລື້ອຍໆມະຫັດສະຈັນເອກອັກຄະລັດຖະທູດ',
    r = s.match(/(?:(?!ະ).)+?(?:ະ|(?=[ໃໄໂເແ]|$))/g);

console.log(r); //=> [ 'ເລື້ອຍໆມະ', 'ຫັດສະ', 'ຈັນ', 'ເອກອັກຄະ', 'ລັດຖະ', 'ທູດ' ]

Upvotes: 3

Mark Reed
Mark Reed

Reputation: 95385

If you use parentheses in the delimited regex, the captured text is included in the returned array. So you can just split on /(ະ)/ and then concatenate each of the odd members of the resulting array to the preceding even member. Example:

"ເລື້ອຍໆມະຫັດສະຈັນເອກອັກຄະລັດຖະທູ".split(/(ະ)/).reduce(function(arr,str,index) {
   if (index%2 == 0) { 
     arr.push(str); 
   } else { 
     arr[arr.length-1] += str
   }; 
   return arr;
 },[])

Result: ["ເລື້ອຍໆມະ", "ຫັດສະ", "ຈັນເອກອັກຄະ", "ລັດຖະ", "ທູ"]

You can do another pass to split on the lookahead:

"ເລື້ອຍໆມະຫັດສະຈັນເອກອັກຄະລັດຖະທູ".split(/(ະ)/).reduce(function(arr,str,index) {
   if (index%2 == 0) { 
     arr.push(str); 
   } else { 
     arr[arr.length-1] += str
   }; 
   return arr;
 },[]).reduce(function(arr,str){return arr.concat(str.split(/(?=[ໃໄໂເແ])/));},[]);

Result: ["ເລື້ອຍໆມະ", "ຫັດສະ", "ຈັນ", "ເອກອັກຄະ", "ລັດຖະ", "ທູ"]

Upvotes: 1

Avinash Raj
Avinash Raj

Reputation: 174874

You could try matching rather than splitting,

> var re = /((?:(?!ະ).)+(?:ະ|$))/g;
undefined
> var str = "ເລື້ອຍໆມະຫັດສະຈັນເອກອັກຄະລັດຖະທູດ"
undefined
> var m;
undefined
> while ((m = re.exec(str)) != null) {
... console.log(m[1]);
... }
ເລື້ອຍໆມະ
ຫັດສະ
ຈັນເອກອັກຄະ
ລັດຖະ
ທູດ

Then again split the elements in the array using lookahead.

Upvotes: 1

Related Questions