javascript javascript函数参数中的下划线是什么意思？
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What is the meaning of an Underscore in javascript function parameter?
提问by Azhar
I was going through the code of one of the chart library written in javascript, wherein I've seen passing underscore(_) as a function parameter. What does that mean?
我正在浏览用 javascript 编写的图表库之一的代码，其中我看到将下划线（_）作为函数参数传递。这意味着什么？
e.g.
例如
chart.x = function(_) {
if (!arguments.length) return lines.x;
lines.x(_);
lines2.x(_);
return chart;
};Can someone please update on this...Thanks.
有人可以更新这个...谢谢。
回答by sagar43
The underscore symbol _is a valid identifier in JavaScript, and in your example, it is being used as a function parameter.
下划线符号_是 JavaScript 中的有效标识符，在您的示例中，它被用作函数参数。
A single underscore is a convention used by some javascript programmers to indicate to other programmers that they should "ignore this binding/parameter". Since JavaScript doesn't do parameter-count checking the parameter could have been omitted entirely.
单个下划线是一些 JavaScript 程序员用来向其他程序员表明他们应该“忽略此绑定/参数”的约定。由于 JavaScript 不进行参数计数检查，因此可以完全省略参数。
This symbol is often used (by convention again) in conjunction with fat-arrow functions to make them even terser and readable, like this:
这个符号通常（再次按照惯例）与粗箭头函数结合使用，使它们更简洁易读，如下所示：
const fun = _ => console.log('Hello, World!')
fun()
In this case, the function needs no params to run, so the developer has used the underscore as a convention to indicate this. The same thing could be written like this:
在这种情况下，该函数不需要参数来运行，因此开发人员使用下划线作为约定来表示这一点。同样的事情可以这样写：
const fun = () => console.log('Hello, World!')
fun()
The difference is that the second version is a function with no parameters, but the first version has a parameter called _ that is ignored. These are different though and the second version is safer, if slightly more verbose (1 extra character).
不同的是，第二个版本是一个没有参数的函数，但第一个版本有一个名为 _ 的参数被忽略了。这些是不同的，第二个版本更安全，如果稍微更冗长（1 个额外字符）。
Also, consider a case like
另外，考虑一个案例
arr.forEach(function (_, i) {..})
Where _indicates the first parameter is not to be used.
where_表示不使用第一个参数。
The use of underscores like this can get very confusing when using the popular lodash or underscore libraries.
在使用流行的 lodash 或下划线库时，像这样使用下划线会变得非常混乱。
回答by Anand Raja
_ in fat arrow function is called as throwaway variable. It means that actually we're creating an variable but simply ignoring it. More devs are now a days using this as syntactic sugar or short hand while writing code, as it's easy and one character less to write the code.
_ 在胖箭头函数中被称为一次性变量。这意味着实际上我们正在创建一个变量，但只是忽略了它。现在越来越多的开发人员在编写代码时使用它作为语法糖或速记，因为编写代码很容易并且少一个字符。
Instead of using _, you can use other variables like temp, x, etc
除了使用 _，您还可以使用其他变量，如 temp、x 等
for examples:
举些例子：
() => console.log('Hello World')
_ => console.log('Hello World')
x => console.log('Hello World')
But personally i prefer to use () type over throwaway variable if no arguments are needed.
但我个人更喜欢在不需要参数的情况下使用 () 类型而不是一次性变量。
See the following code, then you will understand it better.
看下面的代码，你会更好地理解它。
_ as an argument,
_ 作为论据，
f = _=> {
return _ + 2 ;
}
f(3) will return 5
f(3) 将返回 5
