mysql⽐较两个数组_⽐较两个数组相等
今天意外地发现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
以上两句代码都会弹出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：
或
请不要使⽤这种⽅法。
这种⽅法在某些情况下是可⾏的，当两个数组的元素顺序相同且元素都可以转换成字符串的情况下确实可⾏，但是这样的代码存有隐患，⽐如数字被转换成字符串，数字“1”和字符串“1”会被认为相等，可能造成调试困难，不推荐使⽤。
在StackOverflow上有⼤神已经提供了正确的⽅法，我就做下搬运⼯吧：
1 // Warn if overriding existing method
2 if(Array.prototype.equals)
3 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.");
4 // attach the .equals method to Array's prototype to call it on any array
5 Array.prototype.equals = function (array) {
6 // if the other array is a falsy value, return
7 if (!array)
8 return false;
9
10 // compare lengths - can save a lot of time
11 if (this.length != array.length)
12 return false;
13
14 for (var i = 0, l = this.length; i < l; i++) {
15 // Check if we have nested arrays
16 if (this[i] instanceof Array && array[i] instanceof Array) {
17 // recurse into the nested arrays
18 if (!this[i].equals(array[i]))
19 return false;
20 }
21 else if (this[i] != array[i]) {
22 // Warning - two different object instances will never be equal: {x:20} != {x:20}
23 return false;
24 }
25 }
26 return true;
27 }
28 // Hide method from for-in loops
29 Object.defineProperty(Array.prototype, "equals", {enumerable: false});
⼤神还顺⼿给了⽐较Object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
//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;
typeof array}
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;
}

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