JavaScript是不能用==或===操作符直接比較兩個陣列是否相等的

alert([]==[]);    // false
alert([]===[]);   // false

因為JavaScript裡面Array是物件，==或===操作符只能比較兩個物件是否是同一個例項，也就是是否是同一個物件引用。目前JavaScript沒有內建的操作符判斷物件的內容是否相同。

但是慣性思維讓人以為陣列也是值，是可以比較的。

如果要比較陣列是否相等，就只能遍歷陣列元素比較。

在網上流傳很普遍的一種做法是將陣列轉換成字串：

JSON.stringify(a1) == JSON.stringify
 
(a2)
a1.toString() == a2.toString()

不能使用這種方式，如果出現物件陣列或者數組裡面巢狀陣列，1和‘1’是分辨不清楚的。並且還要求元素的順序是相同的。

下面搬運別人的比較方法：

// Warn if overriding existing method
  if(Array.prototype.equals)
      console.warn("Overriding existing Array.prototype.equals. Possible causes: 
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});

• 比較物件的方法

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;
}  

搬運自別人。