javascript - 在 JavaScript 等式中使用 HTML 文本框中的数字

Question

所以我有一些 HTML 代码:

<input type="number" id="height">

我想获取在此框中输入的任何内容并将其用作 int/float 等。假设我输入“2”。这是 JavaScript 代码:

var test;
var a;
test = document.getElementById('height').value;
a = 2 + test;

当我打印 a 时，我得到 22。这是有道理的，但我想要 4。换句话说，我希望 test 被视为 int/float(无论在文本框中输入什么)。是否有 HTML 输入类型可以为我执行此操作，或者我是否必须以其他方式更改它(如 JavaScript 命令)。

Answer 1

使用加号 (+) a.k.a unary plus 运算符作为变量赋值的第一个标记(rvalue) , test = +document.getElementById('height').value

来自developer.mozilla.org:

The unary plus operator precedes its operand and evaluates to its operand but attempts to converts it into a number, if it isn't already. Although unary negation (-) also can convert non-numbers, unary plus is the fastest and preferred way of converting something into a number, because it does not perform any other operations on the number. It can convert string representations of integers and floats, as well as the non-string values true, false, and null. Integers in both decimal and hexadecimal ("0x"-prefixed) formats are supported. Negative numbers are supported (though not for hex). If it cannot parse a particular value, it will evaluate to NaN.

工作示例

var test = +document.getElementById("height").value;
var a;

a = 2 + test;
alert(a);

<input type="number" id="height" value="5">