Run results for: Repeating String

Test name	Executions per second
Simple for loop	47869.8 Ops/sec
Extended for loop	54770.8 Ops/sec
Log based	2675591.8 Ops/sec
Array join	32677.6 Ops/sec

Simple for loop

function repeatify(string, repetitions) {
   if (repetitions < 0 || repetitions === Infinity) {
      throw new RangeError('Invalid repetitions number');
   }
 
   let result = '';
 
   for (let i = 0; i < repetitions; i++) {
      result += string;
   }
 
   return result;
}

repeatify('*', 10000);

Extended for loop

function repeatify2(string, repetitions) {
   if (repetitions < 0 || repetitions === Infinity) {
      throw new RangeError('Invalid repetitions number');
   }
 
   const isEven = repetitions % 2 === 0;
   const iterations = Math.floor(repetitions / 2);
   const stringTwice = string + string;
 
   let result = '';
 
   for (let i = 0; i < iterations; i++) {
      result += stringTwice;
   }
 
   if (!isEven) {
      result += string;
   }
 
   return result;
}

repeatify2('*', 10000);

Log based

function repeatify3(string, repetitions) {
   if (repetitions < 0 || repetitions === Infinity) {
      throw new RangeError('Invalid repetitions number');
   }
 
   const cache = new Map();
 
   function repeat(string, repetitions) {
      if (repetitions === 0) {
         return '';
      }
 
      const log = Math.floor(Math.log2(repetitions));
      let result;
 
      if (cache.has(log)) {
         result = cache.get(log);
      } else {
         result = string;
 
         for (let i = 1; i <= log; i++) {
            result += result;
            cache.set(i, result);
         }
      }
 
      const repetitionsProcessed = Math.pow(2, log);
      const repetitionsLeft = repetitions - repetitionsProcessed;
 
      return result + repeat(string, repetitionsLeft);
   }
 
   return repeat(string, repetitions);
}

repeatify3('*', 10000);

Array join

function repeatify4(string, repetitions) {
   if (repetitions < 0 || repetitions === Infinity) {
      throw new RangeError('Invalid repetitions number');
   }
  
  	var resultArray = new Array(repetitions);
 
   for (let i = 0; i < repetitions; i++) {
      resultArray[i] = string;
   }
 

   return resultArray.join('');
   
}

repeatify4('*', 10000);