我有一个javascript字符串到数字转换的问题 [英] I have a problem with a javascript string to number conversion

问题描述

我正在尝试日期，我发现日期类型输入的值

是字符串。我想将返回的字符串的数字部分转换为数字。

我想描述我想要做的最好的方法是粘贴代码。



这里是相关的HTML代码

< input id =dateinputtype =日期> < /输入> 
< input type =buttononclick =calcdiff（）value =submit> < / input> 

这是我的javascript代码。 ctc元素是我测试的地方，看看我是否得到了正确的输出。

 function calcdiff（）{
 var datetest = 。的document.getElementById（ dateinput）值; 
 var yearString = datetest.slice（0,4）; 
 var monthString = datetest.slice（5,7）; 
 var dayString = datetest.slice（8,10）; 
 var yearNum = Number（yearString）; 
 var monthNum = Number（monthString）; 
 var dayNum = Number（dayString）; 
 document.getElementById（ctc）。innerHTML = yearNum; 
 

我的尝试：



当我使用typeof yearNum时，我可以看到它被转换为数字类型。但是，当我在上面的代码中将innerHTML设置为yearNum时，它返回NaN。

即使我将ctc元素设置为显示yearString，它显示2018，如果那是我从日期输入元素中选择的年份。



代码有什么问题，因为它返回NaN并且不是数字？

解决方案

正确的语法应该是

  var  yearNum =  Number （yearString）; 
  var  monthNum =  Number （monthString）; 
  var  dayNum =  Number （dayString）; 

而不是Number（yearString）;因为它试图将字符串yearString转换为数字。非常小的更改，传入yearString变量。



顺便说一下，那些输入元素关闭标签看起来有点奇怪。它应该是

 <  输入    id   =  dateinput    type   =  date  /  >  
 <  输入    type   =  button < span class =code-attribute>   onclick   =  calcdiff（）    value   = 提交  /  >  

I am experimenting with dates and i found out the values from a date type input
are strings. I want to convert the number parts of the string that is returned, to numbers.
I suppose the best way to describe what i am trying to do is by pasting in the code.

here is the relevant HTML code

<input id="dateinput" type="date"> </input>
<input type="button" onclick="calcdiff()" value="submit"> </input>

Here is my javascript code. the ctc element is where i test to see if i get the correct output.

function calcdiff() {
var datetest = document.getElementById("dateinput").value;
  var yearString = datetest.slice(0,4);
  var monthString = datetest.slice(5,7);
  var dayString = datetest.slice(8,10);
var yearNum = Number("yearString");
var monthNum = Number("monthString");
var dayNum = Number("dayString");
document.getElementById("ctc").innerHTML = yearNum;

What I have tried:

when i use typeof yearNum, i can see it is converted to a number type. However,
when i just set the innerHTML to yearNum as in the code above, it returns "NaN".
That is even though if i set the ctc element to display yearString, it displays "2018", if that is the year i choose from the date input element.

What is wrong with the code since it returns "NaN" and not the number?

解决方案

The correct syntax should be

var yearNum = Number(yearString);
  var monthNum = Number(monthString);
  var dayNum = Number(dayString);

and not Number("yearString"); because it try to convert the string "yearString" into number. Very minor changes, pass in the yearString variable.

By the way, those input elements closing tag look a little odd. it should be

<input id="dateinput" type="date"/>
<input type="button" onclick="calcdiff()" value="submit"/>

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