Javascript 如何强制 JS 做数学运算而不是将两个字符串放在一起
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How to force JS to do math instead of putting two strings together
提问by Sean
I need javascript to add 5 to an integer variable, but instead it treats the variable as a string, so it write out the variable, then add 5 onto the end of the "string". How can I force it to do math instead?
我需要 javascript 将 5 添加到一个整数变量中，但它将变量视为字符串，因此它写出变量，然后将 5 添加到“字符串”的末尾。我怎么能强迫它做数学呢？
var dots = document.getElementById("txt").value; // 5
function increase(){
dots = dots + 5;
}
Output: 55
输出： 55
How can I force it to output 10?
我怎样才能强制它输出10？
回答by Alex
You have the line
你有这条线
dots = document.getElementById("txt").value;
in your file, this will set dots to be a string because the contents of txt is not restricted to a number.
在您的文件中，这会将点设置为字符串，因为 txt 的内容不限于数字。
to convert it to an int change the line to:
要将其转换为 int 将行更改为：
dots = parseInt(document.getElementById("txt").value, 10);
Note: The 10here specifies decimal (base-10). Without this some browsers may not interpret the string correctly. See MDN: parseInt.
注意：10此处指定十进制（基数为 10）。如果没有这个，一些浏览器可能无法正确解释字符串。见MDN： parseInt。
回答by mier
the simplest:
最简单的：
dots = dots*1+5;
the dots will be converted to number.
点将被转换为数字。
回答by Nicolas
DON'T FORGET - Use parseFloat();if your dealing with decimals.
不要忘记 -parseFloat();如果您处理小数，请使用。
回答by Christopher Strolia-Davis
I'm adding this answer because I don't see it here.
我添加这个答案是因为我在这里没有看到它。
One way is to put a '+' character in front of the value
一种方法是在值前面放一个“+”字符
example:
例子：
var x = +'11.5' + +'3.5'
x === 15
x === 15
I have found this to be the simplest way
我发现这是最简单的方法
In this case, the line:
在这种情况下，该行：
dots = document.getElementById("txt").value;
could be changed to
可以改为
dots = +(document.getElementById("txt").value);
to force it to a number
将其强制为一个数字
NOTE:
笔记：
+'' === 0
+[] === 0
+[5] === 5
+['5'] === 5
回答by Alan L.
parseInt()should do the trick
parseInt()应该做的伎俩
var number = "25";
var sum = parseInt(number, 10) + 10;
var pin = number + 10;
Gives you
给你
sum == 35
pin == "2510"
http://www.w3schools.com/jsref/jsref_parseint.asp
http://www.w3schools.com/jsref/jsref_parseint.asp
Note: The 10in parseInt(number, 10)specifies decimal (base-10). Without this some browsers may not interpret the string correctly. See MDN: parseInt.
注意：10inparseInt(number, 10)指定十进制（基数为 10）。如果没有这个，一些浏览器可能无法正确解释字符串。见MDN： parseInt。
回答by Holger.Buick
This also works for you:
这也适用于您：
dots -= -5;
回答by Nelson Cajetin Diego Alfonso
its really simple just
它真的很简单
var total = (1 * yourFirstVariablehere) + (1 * yourSecondVariablehere)
this forces javascript to multiply because there is no confusion for * sign in javascript.
这会强制 javascript 成倍增加，因为 * 登录 javascript 没有混淆。
回答by Hassan Ali Salem
You can add + behind the variable and it will force it to be an integer
您可以在变量后面添加 + ，它会强制它是一个整数
var dots = 5
function increase(){
dots = +dots + 5;
}
回答by Jay Reeve
After trying most of the answers here without success for my particular case, I came up with this:
在针对我的特定案例尝试了大部分答案但没有成功之后，我想出了这个：
dots = -(-dots - 5);
The + signs are what confuse js, and this eliminates them entirely. Simple to implement, if potentially confusing to understand.
+ 符号使 js 感到困惑，这完全消除了它们。实施起来很简单，但可能会让人难以理解。
回答by vapcguy
UPDATED since this was last downvoted....
自上次被否决以来已更新....
I only saw the portion
我只看到了部分
var dots = 5
function increase(){
dots = dots+5;
}
before, but it was later shown to me that the txtbox feeds the variable dots. Because of this, you will need to be sure to "cleanse" the input, to be sure it only has integers, and not malicious code.
之前，但后来向我展示了该txt框提供了变量dots. 因此，您需要确保“清理”输入，以确保它只有整数，而不是恶意代码。
One easy way to do this is to parse the textbox with an onkeyup()event to ensure it has numeric characters:
一种简单的方法是使用onkeyup()事件解析文本框以确保它具有数字字符：
<input size="40" id="txt" value="Write a character here!" onkeyup="GetChar (event);"/>
where the event would give an error and clear the last character if the value is not a number:
如果值不是数字，事件将给出错误并清除最后一个字符：
<script type="text/javascript">
function GetChar (event){
var keyCode = ('which' in event) ? event.which : event.keyCode;
var yourChar = String.fromCharCode();
if (yourChar != "0" &&
yourChar != "1" &&
yourChar != "2" &&
yourChar != "3" &&
yourChar != "4" &&
yourChar != "5" &&
yourChar != "6" &&
yourChar != "7" &&
yourChar != "8" &&
yourChar != "9")
{
alert ('The character was not a number');
var source = event.target || event.srcElement;
source.value = source.value.substring(0,source.value-2);
}
}
</script>
Obviously you could do that with regex, too, but I took the lazy way out.
显然你也可以用正则表达式来做到这一点，但我采取了懒惰的方式。
Since then you would know that only numbers could be in the box, you should be able to just use eval():
从那时起，您就会知道框中只能包含数字，您应该可以使用eval()：
dots = eval(dots) + 5;
