javascript函数参数中的下划线是什么意思? [英] What is the meaning of an Underscore in javascript function parameter?

问题描述

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(_)作为函数参数进行传递.是什么意思?

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?

例如

chart.x = function(_) {
    if (!arguments.length) return lines.x;
    lines.x(_);
    lines2.x(_);
    return chart;
  };

有人可以对此进行更新吗...谢谢.

Can someone please update on this...Thanks.

推荐答案

下划线符号_在JavaScript中是有效的标识符，在您的示例中，它被用作函数参数.

The underscore symbol _ is a valid identifier in JavaScript, and in your example, it is being used as a function parameter.

单个下划线是一些Javascript程序员用来向其他程序员指示他们应该忽略此绑定/参数"的约定.由于JavaScript不会进行参数计数检查，因此可以完全省略该参数.

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.

此符号通常(再次按照惯例)与fat-arrow函数结合使用，以使它们更简洁易读，如下所示:

This symbol is often used (by convention again) in conjunction with fat-arrow functions to make them even terser and readable, like this:

const fun = _ => console.log('Hello, World!')
fun()

在这种情况下，该函数不需要运行任何参数，因此开发人员已使用下划线作为惯例来表明这一点.可以这样写同样的东西:

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:

const fun = () => console.log('Hello, World!')
fun()

区别在于第二个版本是不带参数的函数，但是第一个版本有一个名为_的参数，该参数将被忽略.但是，它们有所不同，第二个版本比较冗长(多了1个字符)，因此比较安全.

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).

还要考虑类似

arr.forEach(function (_, i) {..})

_表示不使用第一个参数.

Where _ indicates the first parameter is not to be used.

在使用流行的lodash或下划线库时，使用这样的下划线会造成混乱.

The use of underscores like this can get very confusing when using the popular lodash or underscore libraries.

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