Keep only one occurrence of substring in a string

Question

I'm looking for a function that removes all occurrences of a substring in a string except the first one, so for example

function keepFirst(str, substr) { ... }
keepFirst("This $ is some text $.", "$");

should return: This $ is some text .

I could do it using split() and then for(){} , but is there a nicer solution?

Answer 1

This solution finds the index of the first occurence of rep and removes all of the rep s after it.

 console.log(keepFirst("This $ is some text $$ with $ signs.", "$")); function keepFirst(str, rep) { var fInd = str.indexOf(rep); var first = str.substring(0, fInd + rep.length); var rest = str.substring(fInd + rep.length); return first + rest.replace( new RegExp(rep.replace(/[.*+?^${}()|[\\]\\\\]/g, "\\\\$&"), 'g'), ''); } 

Answer 2

This could be the shortest code that is somewhat efficient. It uses destructuring assignment .

function keepFirst(str, substr) {
  const [
    first,
    ...rest
  ] = str.split(substr);

  return first + (rest.length
    ? substr + rest.join("")
    : "");
}