Match a regular expression to an array of characters

Question

on the page I'm creating, I need to have a string ring buffer with a specific size. I use an array for this purpose and just push and not switch. one index is a single character. I do not want to use a string since as soon as I push a character to the buffer, a copy occurs. Now I need to use the regex in this buffer. The problem is that now every time I want to match, I need array.join()it to be expensive ...

Now I am wondering if it is possible to directly use a regular expression in an array of characters instead of first converting it to a string.

I guess if a mutable string type existed, I would never have this problem ...

Answer 1

Agreed..! JS strings are immutable, however your concerns about their concatenation, which are time consuming, are not well-founded. I can confirm that both in Chrome, Firefox, Opera, IE11, and Safari a Array.prototype.join()operation on an array of 1,000,000 random characters takes about 10 ~ 40 ms depending on the engine. Yes ... like that. (especially Spider Monkey is shining). Take a look

var   arr = [],
    match = [],
  longStr = "",
    count = 1000000,
    start = 0,
      end = 0;

for (var i=0; i<count; i++){
  arr.push((+new Date()*Math.random()).toString(36)[0]);
}
start = performance.now();
longStr = arr.join("");
end = performance.now();
console.log("Concatenation took "+(end-start)+" msecs");
// Concatenation took 10.875 msecs.. Wow Firefox..!
start = performance.now();
match = longStr.match(/7{5,}/g);
!match && (match = [])
end = performance.now();
console.log("Regex match took "+(end-start)+" msecs and found " +match.length+" matches as: ", match);
//Regex match took 6.550000000046566 msecs and found 1 matches as: ["77777"]

, , . . . , Array.prototype. , primitiveValue, , length, this.primitiveValue = this.join();, Array.prototype, length, primitiveValue. , . , , primitiveValue. , length , . RingBuffer.prototype , primitiveValue . .

function RingBuffer(){
    this.primitiveValue = "";
    this.__len;
    Object.defineProperty(this, "length", {
                                             enumerable: true,
                                           configurable: true,
                                                    get: this.getLength,
                                                    set: this.setLength
                                          });
}
RingBuffer.prototype = Array.prototype;
RingBuffer.prototype.constructor = RingBuffer;
RingBuffer.prototype.getLength = function(){
                                   return this.__len;
                                 };
RingBuffer.prototype.setLength = function(val){
                                   this.__len = val;
                                   this.primitiveValue = this.join("");
                                 };
var ringu = new RingBuffer();

, ringu 100 000 . Chrome 49 :

var longStr = "",
      count = 100000,
      start = performance.now(),
        end = 0;
for (var i=1; i<=count; i++){
  ringu.push((+new Date()*Math.random()).toString(36)[0]);
  if (!(i % 10000)){
    end = performance.now();
    console.log(i/10000+". 10000 pushes done at :"+(end - start)+" msecs");
    start = end;
  }
}
console.log("ringu is filled with " + count + " random characters");
start = performance.now();
longStr = ringu.join("");
end = performance.now();
console.log("Last concatenation took "+(end-start)+" msecs");

1. 10000 pushes done at :1680.6399999996647 msecs
2. 10000 pushes done at :4873.2599999997765 msecs
3. 10000 pushes done at :8044.155000000261 msecs
4. 10000 pushes done at :11585.525000000373 msecs
5. 10000 pushes done at :14642.490000000224 msecs
6. 10000 pushes done at :17998.389999999665 msecs
7. 10000 pushes done at :20814.979999999516 msecs
8. 10000 pushes done at :24024.445000000298 msecs
9. 10000 pushes done at :27146.375 msecs
10. 10000 pushes done at :30347.794999999925 msecs
ringu is filled with 100000 random characters
Last concatenation took 3.510000000707805 msecs

, , primitiveValue , , this.join("");. 500K RingBuffer 30 .

... SpiderMonkey. , Node.Js, , JXCore, Spider Monkey ChakraCore Node V8.

1. 10000 pushes done at :710.310000000005 msecs
2. 10000 pushes done at :1831.4599999999991 msecs
3. 10000 pushes done at :3018.199999999997 msecs
4. 10000 pushes done at :4113.779999999999 msecs
5. 10000 pushes done at :5144.470000000008 msecs
6. 10000 pushes done at :6588.179999999993 msecs
7. 10000 pushes done at :7860.005000000005 msecs
8. 10000 pushes done at :8727.050000000003 msecs
9. 10000 pushes done at :9795.709999999992 msecs
10. 10000 pushes done at :10866.055000000008 msecs
ringu is filled with 100000 random characters
Last concatenation took 1.0999999999912689 msecs