JavaScript 中比较数组与对象是否相等的实现方法

JSON.stringify([1,2,3].sort()) === JSON.stringify([3,2,1].sort());

[1,2,3].sort().toString() === [3,2,1].sort().toString();

let cmp = ( x, y ) => {
// If both x and y are null or undefined and exactly the same
 if ( x === y ) {
  return true;
 }
// If they are not strictly equal, they both need to be Objects
 if ( ! ( x instanceof Object ) || ! ( y instanceof Object ) ) {
  return false;
 }
//They must have the exact same prototype chain,the closest we can do is
//test the constructor.
 if ( x.constructor !== y.constructor ) {
  return false;
 }
 for ( var p in x ) {
  //Inherited properties were tested using x.constructor === y.constructor
  if ( x.hasOwnProperty( p ) ) {
  // Allows comparing x[ p ] and y[ p ] when set to undefined
  if ( ! y.hasOwnProperty( p ) ) {
   return false;
  }
  // If they have the same strict value or identity then they are equal
  if ( x[ p ] === y[ p ] ) {
   continue;
  }
  // Numbers, Strings, Functions, Booleans must be strictly equal
  if ( typeof( x[ p ] ) !== "object" ) {
   return false;
  }
  // Objects and Arrays must be tested recursively
  if ( ! Object.equals( x[ p ], y[ p ] ) ) {
   return false;
  }
  }
 }
 for ( p in y ) {
  // allows x[ p ] to be set to undefined
  if ( y.hasOwnProperty( p ) && ! x.hasOwnProperty( p ) ) {
  return false;
  }
 }
 return true;
};

// Warn if overriding existing method
if(Array.prototype.equals)
 console.warn("Overriding existing Array.prototype.equals. Possible causes: New API defines the method, there's a framework conflict or you've got double inclusions in your code.");
// attach the .equals method to Array's prototype to call it on any array
Array.prototype.equals = function (array) {
 // if the other array is a falsy value, return
 if (!array)
  return false;

 // compare lengths - can save a lot of time 
 if (this.length != array.length)
  return false;

 for (var i = 0, l = this.length; i < l; i++) {
  // Check if we have nested arrays
  if (this[i] instanceof Array && array[i] instanceof Array) {
   // recurse into the nested arrays
   if (!this[i].equals(array[i]))
    return false;  
  }   
  else if (this[i] != array[i]) { 
   // Warning - two different object instances will never be equal: {x:20} != {x:20}
   return false; 
  }   
 }  
 return true;
}
// Hide method from for-in loops
Object.defineProperty(Array.prototype, "equals", {enumerable: false});

Object.prototype.equals = function(object2) {
  //For the first loop, we only check for types
  for (propName in this) {
    //Check for inherited methods and properties - like .equals itself
    //https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/hasOwnProperty
    //Return false if the return value is different
    if (this.hasOwnProperty(propName) != object2.hasOwnProperty(propName)) {
      return false;
    }
    //Check instance type
    else if (typeof this[propName] != typeof object2[propName]) {
      //Different types => not equal
      return false;
    }
  }
  //Now a deeper check using other objects property names
  for(propName in object2) {
    //We must check instances anyway, there may be a property that only exists in object2
      //I wonder, if remembering the checked values from the first loop would be faster or not 
    if (this.hasOwnProperty(propName) != object2.hasOwnProperty(propName)) {
      return false;
    }
    else if (typeof this[propName] != typeof object2[propName]) {
      return false;
    }
    //If the property is inherited, do not check any more (it must be equa if both objects inherit it)
    if(!this.hasOwnProperty(propName))
     continue;

    //Now the detail check and recursion

    //This returns the script back to the array comparing
    /**REQUIRES Array.equals**/
    if (this[propName] instanceof Array && object2[propName] instanceof Array) {
          // recurse into the nested arrays
      if (!this[propName].equals(object2[propName]))
            return false;
    }
    else if (this[propName] instanceof Object && object2[propName] instanceof Object) {
          // recurse into another objects
          //console.log("Recursing to compare ", this[propName],"with",object2[propName], " both named \""+propName+"\"");
      if (!this[propName].equals(object2[propName]))
            return false;
    }
    //Normal value comparison for strings and numbers
    else if(this[propName] != object2[propName]) {
      return false;
    }
  }
  //If everything passed, let's say YES
  return true;
}