如何在日期数组中正确使用 JavaScript indexOf
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How to correctly use JavaScript indexOf in a date array
提问by Blaise
Here is the code:
这是代码：
var collection = [new Date(2014, 11, 25), new Date(2014, 11, 24)];
var d=new Date(2014, 11, 24);
var idx= collection.indexOf(d);
I guess the variable idxshould have a value of 1since it is the second value in the array collection. But it turns out to be -1.
我猜这个变量idx应该有一个值，1因为它是数组中的第二个值collection。但事实证明是-1。
Why is that? Is there any special thing for the JavaScript Datetype I need to pay attention?
这是为什么？JavaScriptDate类型有什么特别需要注意的地方吗？
Here is a snippet:
这是一个片段：
(function() {
var collection = [new Date(2014, 11, 25), new Date(2014, 11, 24)];
var d = new Date(2014, 11, 24);
var idx1 = collection.indexOf(d);
var intArray = [1, 3, 4, 5];
var idx2 = intArray.indexOf(4);
$('#btnTry1').on('click', function() {
$('#result1').val(idx1);
});
$('#btnTry2').on('click', function() {
$('#result2').val(idx2);
});
})();<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
Index:
<input type="text" id="result1" value="">
<button id="btnTry1">Find index in a date array</button>
<br />Index:
<input type="text" id="result2" value="">
<button id="btnTry2">Find index in a regular array</button>回答by Paul S.
Two Objectswill never be equal unless you serialise them. Lucky, Dateis pretty easy to serialise as an integer.
除非您将它们序列化，否则两个对象永远不会相等。幸运的是，Date很容易序列化为整数。
var collection = [new Date(2014, 11, 25), new Date(2014, 11, 24)],
d = new Date(2014, 11, 24),
idx;
idx = collection.map(Number).indexOf(+d); // 1
// ^^^^^^^^^^^^ ^ serialisation steps
回答by Felix Kling
Two different objects are never equal to each other, even if they have the same properties / values. Here is a forward looking answer to the problem:
两个不同的对象永远不会彼此相等，即使它们具有相同的属性/值。这是该问题的前瞻性答案：
ECMAScript 6 introduces Array#findIndexwhich accepts a comparison callback:
ECMAScript 6 引入了Array#findIndex它接受比较回调：
var index = collection.findIndex(function(x) {
return x.valueOf() === d.valueOf();
});
回答by LcSalazar
indexOf()won't work here... It's been well explained in the previous answers...
indexOf()在这里不起作用......在以前的答案中已经很好地解释了......
You'd be able to create your own lookup for the index. Here's a simple example comparing the dates using their .getTime()value...
您可以为索引创建自己的查找。这是一个使用日期比较日期的简单示例.getTime()...
(function() {
var collection = [new Date(2014, 11, 25), new Date(2014, 11, 24)];
var d = new Date(2014, 11, 24);
var idx1 = -1;
collection.forEach(function(item, index){
if(d.getTime() == item.getTime())
idx1 = index;
});
var intArray = [1, 3, 4, 5];
var idx2 = intArray.indexOf(4);
$('#btnTry1').on('click', function() {
$('#result1').val(idx1);
});
$('#btnTry2').on('click', function() {
$('#result2').val(idx2);
});
})();<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
Index:
<input type="text" id="result1" value="">
<button id="btnTry1">Find index in a date array</button>
<br />Index:
<input type="text" id="result2" value="">
<button id="btnTry2">Find index in a regular array</button>回答by Freez
Array.prototype.indexOfDate = function(date){
for (var i = 0; i < this.length; i++){
if (+this[i] === +date) return i;
};
return -1;
};
// then
var idx1 = collection.indexOfDate(d);
回答by Seva Arkhangelskiy
This is because your "d" object is the different object. In other words:
这是因为您的“d”对象是不同的对象。换句话说：
var d = new Date(2014, 11, 24);
d === new Date(2014, 11, 24); // returns false
You can try this:
你可以试试这个：
var d = new Date(2014, 11, 24);
var collection = [new Date(2014, 11, 25), d];
var idx = collection.indexOf(d); // returns 1
