比较两个数组和对象是否相同

JavaScript是不能用==或===操作符直接比较两个数组是否相等的

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

因为JavaScript里面Array是对象，==或===操作符只能比较两个对象是否是同一个实例，也就是是否是同一个对象引用。目前JavaScript没有内置的操作符判断对象的内容是否相同。

但是惯性思维让人以为数组也是值，是可以比较的。

如果要比较数组是否相等，就只能遍历数组元素比较。

在网上流传很普遍的一种做法是将数组转换成字符串：

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

不能使用这种方式，如果出现对象数组或者数组里面嵌套数组，1和‘1’是分辨不清楚的。并且还要求元素的顺序是相同的。

下面搬运别人的比较方法：

// 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});

比较对象的方法

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;
}

搬运自别人。