Run results for: Compare sorted versus unsorted keys

Run details:
User agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/99.0.4844.51 Safari/537.36
Browser: Chrome 99
Operating system: Mac OS X 10.15.7
Device Platform: Desktop
Date tested: 2 years ago
Test name	Executions per second
sorted keys	53.6 Ops/sec
for in	68.0 Ops/sec
Script Preparation code:
const alpha = 'abcdefghijklmnopqrstuvwxyz';
const keys = [];

for( let i = 0; i < alpha.length; i++ ) {
  for( let j = 0; j < alpha.length; j++ ) {
    for( let k = 0; k < alpha.length; k++ ) {
  		keys.push( alpha[ i ] + alpha[ j ] + alpha[ k ] );
    }
  }
}

function shuffle(array) {
  let currentIndex = array.length,  randomIndex;

  // While there remain elements to shuffle...
  while (currentIndex != 0) {

    // Pick a remaining element...
    randomIndex = Math.floor(Math.random() * currentIndex);
    currentIndex--;

    // And swap it with the current element.
    [array[currentIndex], array[randomIndex]] = [
      array[randomIndex], array[currentIndex]];
  }

  return array;
}

function fill( obj ) {
  shuffle( keys ).forEach( key => {
    obj[ key ] = key;
  } );
  return obj;
}

function areEquivalent1( value1, value2, stack = [] ) {
  // Numbers, strings, null, undefined, symbols, functions, booleans.
  // Also: objects (incl. arrays) that are actually the same instance
  if ( value1 === value2 ) return true;

  const type1 = typeof value1;

  // Ensure types match
  if ( type1 !== typeof value2 ) return false;

  // Special case for number: check for NaN on both sides
  // (only way they can still be equivalent but not equal)
  if ( type1 === 'number' ) {
    // Failed initial equals test, but could still both be NaN
    return ( isNaN( value1 ) && isNaN( value2 ) );
  }

  // Special case for function: check for toString() equivalence
  if ( type1 === 'function' ) {
    // Failed initial equals test, but could still have equivalent
    // implementations - note, will match on functions that have same name
    // and are native code: `function abc() { [native code] }`
    return value1.toString() === value2.toString();
  }

  // For these types, cannot still be equal at this point, so fast-fail
  if (
    type1 === 'bigint' ||
    type1 === 'boolean' ||
    type1 === 'function' ||
    type1 === 'string' ||
    type1 === 'symbol'
  ) {
    return false;
  }

  // For dates, cast to number and ensure equal or both NaN (note, if same
  // exact instance then we're not here - that was checked above)
  if ( value1 instanceof Date ) {
    if ( !( value2 instanceof Date ) ) {
      return false;
    }
    // Convert to number to compare
    const asNum1 = +value1, asNum2 = +value2;
    // Check if both invalid (NaN) or are same value
    return asNum1 === asNum2 || ( isNaN( asNum1 ) && isNaN( asNum2 ) );
  }

  // At this point, it's a reference type and could be circular, so
  // make sure we haven't been here before... note we only need to track value1
  // since value1 being un-circular means value2 will either be equal (and not
  // circular too) or unequal whether circular or not.
  if ( stack.includes( value1 ) ) {
    throw new Error( `areEquivalent value1 is circular` );
  }

  // breadcrumb
  stack.push( value1 );

  // Handle arrays
  if ( Array.isArray( value1 ) ) {
    if ( !Array.isArray( value2 ) ) {
      return false;
    }

    const length = value1.length;

    if ( length !== value2.length ) return false;

    for ( let i = 0; i < length; i++ ) {
      if ( !areEquivalent1( value1[ i ], value2[ i ], stack ) ) {
        return false;
      }
    }

    // 
    return true;
  }

  // Final case: object

  // get both key lists and check length
  const keys1 = Object.keys( value1 );
  const keys2 = Object.keys( value2 );
  const numKeys = keys1.length;
  
  if ( numKeys !== keys2.length ) {
    return false;
  }

  // Empty object on both sides?
  if ( numKeys === 0 ) {
    return true;
  }

  // sort is a native call so it's very fast - much faster than comparing the
  // values at each key if it can be avoided, so do the sort and then
  // ensure every key matches at every index
  // *** benchmark this vs for (var prop in obj)
  keys1.sort();
  keys2.sort();

  // Ensure perfect match across all keys
  for( let i = 0; i < numKeys; i++ ) {
    if( keys1[ i ] !== keys2[ i ] ) {
      return false;
    }
  }

  // Ensure perfect match across all values
  for( let i = 0; i < numKeys; i++ ) {
    if ( !areEquivalent1( value1[ keys1[ i ] ], value2[ keys1[ i ] ], stack ) ) {
      return false;
    }
  }

  // back up
  stack.pop();

  return true;
}

function areEquivalent2( value1, value2, stack = [] ) {
  // Numbers, strings, null, undefined, symbols, functions, booleans.
  // Also: objects (incl. arrays) that are actually the same instance
  if ( value1 === value2 ) return true;

  const type1 = typeof value1;

  // Ensure types match
  if ( type1 !== typeof value2 ) return false;

  // Special case for number: check for NaN on both sides
  // (only way they can still be equivalent but not equal)
  if ( type1 === 'number' ) {
    // Failed initial equals test, but could still both be NaN
    return ( isNaN( value1 ) && isNaN( value2 ) );
  }

  // Special case for function: check for toString() equivalence
  if ( type1 === 'function' ) {
    // Failed initial equals test, but could still have equivalent
    // implementations - note, will match on functions that have same name
    // and are native code: `function abc() { [native code] }`
    return value1.toString() === value2.toString();
  }

  // For these types, cannot still be equal at this point, so fast-fail
  if (
    type1 === 'bigint' ||
    type1 === 'boolean' ||
    type1 === 'function' ||
    type1 === 'string' ||
    type1 === 'symbol'
  ) {
    return false;
  }

  // For dates, cast to number and ensure equal or both NaN (note, if same
  // exact instance then we're not here - that was checked above)
  if ( value1 instanceof Date ) {
    if ( !( value2 instanceof Date ) ) {
      return false;
    }
    // Convert to number to compare
    const asNum1 = +value1, asNum2 = +value2;
    // Check if both invalid (NaN) or are same value
    return asNum1 === asNum2 || ( isNaN( asNum1 ) && isNaN( asNum2 ) );
  }

  // At this point, it's a reference type and could be circular, so
  // make sure we haven't been here before... note we only need to track value1
  // since value1 being un-circular means value2 will either be equal (and not
  // circular too) or unequal whether circular or not.
  if ( stack.includes( value1 ) ) {
    throw new Error( `areEquivalent value1 is circular` );
  }

  // breadcrumb
  stack.push( value1 );

  // Handle arrays
  if ( Array.isArray( value1 ) ) {
    if ( !Array.isArray( value2 ) ) {
      return false;
    }

    const length = value1.length;

    if ( length !== value2.length ) return false;

    for ( let i = 0; i < length; i++ ) {
      if ( !areEquivalent2( value1[ i ], value2[ i ], stack ) ) {
        return false;
      }
    }

    // 
    return true;
  }

  // Final case: object

  // get both key lists and check length
  const keys1 = Object.keys( value1 );
  const numKeys = keys1.length;
  
  if ( numKeys !== Object.keys( value2 ).length ) {
    return false;
  }

  // Empty object on both sides?
  if ( numKeys === 0 ) {
    return true;
  }

  let matches = 0;
  
  // Ensure perfect match across all keys
  for( let key in value1 ) {
    if( key in value2 ) matches++;
    else return false;
  }
  
  if( matches < numKeys ) return false;

  // Ensure perfect match across all values
  for( let key in value1 ) {
    if ( !areEquivalent2( value1[ key ], value2[ key ], stack ) ) {
      return false;
    }
  }

  // back up
  stack.pop();

  return true;
}
Tests:
sorted keys
const equivalent = areEquivalent1( fill( {} ), fill( {} ) );
for in
const equivalent = areEquivalent2( fill( {} ), fill( {} ) );
Run results for: Compare sorted versus unsorted keys

sorted keys

for in
