性能慢的自定义脚本 GAS

Question

So, I've written (for lack of answers + improving my skills) a search script that would do basically what.indexOf does.

function search(ref, data) {

  var x
  var y
  var result = []

  if (data == '' || data == null) {
  } else {
    for (x = 0; x < data.length; x++) {
      if (data[x] == ref[0]) {                //achando match inicial
        var proto = [];
        for (y = 0; y < ref.length; y++) {
          if (data[x+y] == ref[y]) {          //gravando tentativas de match completo
          proto.push(data[x+y])
          }
        }
        var proto2 = proto.join('')
        if (proto2 == ref) {                   //testando match completo
            result.push(x)
        }
      }
    }
  }
  if (result == '' || result == null) {
  } else {
    return result[0]
  }
}

It works fine within other little codes and custom functions that do not require too much looping, but when I wrote a more robust script I found that my code is roughly 3000x slower than the native.indeOf.

Why would I incur in such a difference?

Answer 1

Issue:

Your function is comparing each character from ref separately with a data character, in an inner loop, pushing each character match inside an array ( proto ) and using join to transform the array back to a string ( proto2 ), before comparing it to the original ref .

This is extremely inefficient and could be greatly simplified, so no question this function is much slower than String.prototype.indexOf() .

Solution:

You could have a single loop instead, iterating through data , and for each iteration, retrieve a slice of data with the same length as ref , before comparing this slice with ref . If both values match, the string ref has been found in data , and the corresponding index is returned:

function searchString(ref, data) {
  for (let i = 0; i <= data.length - ref.length; i++) {
    if (ref === data.slice(i, i + ref.length)) return i;
  }
  return -1;
}

While using this function, I get similar execution times than with indexOf .

Reference:

• String.prototype.indexOf()
• String.prototype.slice()