Javascript jquery中的简单数学
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Simple math in jquery
提问by Darren
I am reading a select form value and multiplying it by 50 in jquery. I need to add a value of 1 to the qty that is returned by the select menu every time before multiplying by 50. How would I do that? The offending code looks like this.
我正在读取一个选择表单值并在 jquery 中将其乘以 50。我需要在每次乘以 50 之前将值 1 添加到选择菜单返回的数量上。我该怎么做？违规代码如下所示。
$('#selectform').val() *50);
If I use
如果我使用
$('#selectform').val() +1 *50);
The result is not correct.
结果不正确。
回答by Rob W
Parentheses should be used.
应该使用括号。
($('#selectform').val()*1 + 1) *50;
Your current expression is interpreted as:
您当前的表达式被解释为：
var something = $('#selectform').val();
var another = 1 * 50;
var result = something + another
The *1after .val()is used to convert the string value to a number. If it's omitted, the expression will be interpreted as:
在*1之后.val()用来将字符串值转换为数字。如果省略，则表达式将被解释为：
var something = $('#selectform').val() + "1"; //String operation
var result = something * 50; // something is converted to a number, and
// multiplied by 50
回答by rogerlsmith
The data from $('#selectform').val()is probably being treated as a string.
Use parseInt($('#selectform').val())to convert it to an int before the multiply.
来自的数据$('#selectform').val()可能被视为字符串。
用于parseInt($('#selectform').val())在乘法之前将其转换为 int。
回答by Jayendra
Correct parentheses and use parseInt function -
更正括号并使用 parseInt 函数 -
(parseInt($('#selectform').val(),10) +1) *50;
回答by Cito
You should have a look at the operator precedence in JavaScript.
您应该看看JavaScript中的运算符优先级。
回答by swatkins
You need to force the addition to happen before the multiplication with parentheses:
您需要在带括号的乘法之前强制加法：
bar myVal = ($("#selectform").val() + 1) * 50;
