[英]What is the meaning of an Underscore in javascript function parameter?
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.我正在浏览一个用 javascript 编写的图表库的代码,其中我看到将下划线( _
)作为函数参数传递。 What does that mean?这意味着什么?
chart.x = function(_) { if (!arguments.length) return lines.x; lines.x(_); lines2.x(_); return chart; };
Can someone please update on this...Thanks.有人可以请更新这...谢谢。
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".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。 Since JavaScript doesn't do parameter-count checking the parameter could have been omitted entirely.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.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。 The same thing could be written like this:同样的事情可以写成这样:
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.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。 These are different though and the second version is safer, if slightly more verbose (1 extra character).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.其中_
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。
_ in fat arrow function is called as throwaway variable . _ 在胖箭头函数中被称为一次性变量。 It means that actually we're creating an variable but simply ignoring it.这意味着实际上我们正在创建一个变量,但只是忽略了它。 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.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
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