Run results for: Repeating String

Run details:

User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:50.0) Gecko/20100101 Firefox/50.0

Browser: Firefox 50

Operating system: Mac OS X 10.12

Device Platform: Other

Date tested: 8 years ago

Test name	Executions per second
Simple for loop	6040.2 Ops/sec
Extended for loop	11658.2 Ops/sec
Log based	127897.6 Ops/sec
Array approach	1041.9 Ops/sec

Tests:

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);

​x
 
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);

 
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);

 
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 approach

function repeatify4(string, repetitions) {
   if (repetitions < 0 || repetitions === Infinity) {
      throw new RangeError('Invalid repetitions number');
   }
 
   return Array(repetitions + 1).join(string);
}

repeatify4('*', 10000);

 
function repeatify4(string, repetitions) {   if (repetitions < 0 || repetitions === Infinity) {      throw new RangeError('Invalid repetitions number');   }    return Array(repetitions + 1).join(string);}​repeatify4('*', 10000);