在闭包中为局部变量赋值(Assigning arguments to local variables in closure)

在闭包中为局部变量赋值(Assigning arguments to local variables in closure)

这是一个来自javascript模式的currying片段：

function add(x, y) { var oldx = x, oldy = y; if (typeof oldy === "undefined") { // partial return function (newy) { return oldx + newy; } } // full application return x + y; }

参考： https ： //github.com/shichuan/javascript-patterns/blob/master/function-patterns/currying.html

当地的vars oldx和oldy有什么意义？

Here is a currying snippet from javascript patterns:

function add(x, y) { var oldx = x, oldy = y; if (typeof oldy === "undefined") { // partial return function (newy) { return oldx + newy; } } // full application return x + y; }

ref: https://github.com/shichuan/javascript-patterns/blob/master/function-patterns/currying.html

What is the point of local vars oldx and oldy?

最满意答案

这里完全没有变量oldx和oldy ; 代码在没有它们的情况下表现相同：

function add(x, y) { if (typeof y === "undefined") { // partial return function (y) { return x + y; } } // full application return x + y; }

此处返回的函数可以访问外部作用域变量，无论这些变量是使用var声明还是声明为外部函数的形式参数。

一般来说，如果x是基元，如果您需要该值的副本以独立于原始值进行更改，则有时将其分配给新变量是有意义的：

function foo(x) { var newX = x; newX += 7; // now newX and x are different // ... }

但是 ，此代码中不存在该需求，因此完全没有必要。

The variables oldx and oldy are completely unnecessary here; the code behaves identically without them:

function add(x, y) { if (typeof y === "undefined") { // partial return function (y) { return x + y; } } // full application return x + y; }

The function being returned here has access to outer-scope variables regardless of whether those variables are declared with var or declared as formal arguments to an outer function.

Generally speaking, if x is a primitive, it might sometimes make sense to assign it to a new variable if you needed a copy of that value to alter independently of the original:

function foo(x) { var newX = x; newX += 7; // now newX and x are different // ... }

However, that need does not exist in this code, so it's totally unnecessary.