递归调用javascript函数 [英] Calling a javascript function recursively

问题描述

我可以像这样在变量中创建递归函数:

I can create a recursive function in a variable like so:

/* Count down to 0 recursively.
 */
var functionHolder = function (counter) {
    output(counter);
    if (counter > 0) {
        functionHolder(counter-1);
    }
}

这样，functionHolder(3); 将输出 3 2 1 0.假设我做了以下事情:

With this, functionHolder(3); would output 3 2 1 0. Let's say I did the following:

var copyFunction = functionHolder;

copyFunction(3); 将输出 3 2 1 0 为以上.如果我将 functionHolder 更改如下:

copyFunction(3); would output 3 2 1 0 as above. If I then changed functionHolder as follows:

functionHolder = function(whatever) {
    output("Stop counting!");

然后 functionHolder(3); 会按预期给出 停止计数！.

Then functionHolder(3); would give Stop counting!, as expected.

copyFunction(3); 现在给出 3 停止计数！ 因为它指的是 functionHolder，而不是函数(它本身指向).在某些情况下这可能是可取的，但有没有办法编写函数，使其调用自身而不是保存它的变量?

copyFunction(3); now gives 3 Stop counting! as it refers to functionHolder, not the function (which it itself points to). This could be desirable in some circumstances, but is there a way to write the function so that it calls itself rather than the variable that holds it?

也就是说，是否可以更改仅行functionHolder(counter-1);，以便通过所有这些步骤仍然得到3 2 1 0 当我们调用 copyFunction(3); 时?我试过 this(counter-1); 但这给了我错误 this is not a function.

That is, is it possible to change only the line functionHolder(counter-1); so that going through all these steps still gives 3 2 1 0 when we call copyFunction(3);? I tried this(counter-1); but that gives me the error this is not a function.

推荐答案

使用命名函数表达式:

您可以为函数表达式指定一个实际上私有的名称，并且仅在函数内部可见:

Using Named Function Expressions:

You can give a function expression a name that is actually private and is only visible from inside of the function ifself:

var factorial = function myself (n) {
    if (n <= 1) {
        return 1;
    }
    return n * myself(n-1);
}
typeof myself === 'undefined'

此处myself仅在函数内部可见.

您可以使用此私有名称递归调用该函数.

You can use this private name to call the function recursively.

参见 13.ECMAScript 5 规范的函数定义:

可以从 FunctionExpression 的 FunctionBody 内部引用 FunctionExpression 中的 Identifier，以允许函数递归调用自身.但是，与 FunctionDeclaration 不同的是，FunctionExpression 中的 Identifier 不能被引用并且不会影响包含 FunctionExpression 的范围.

The Identifier in a FunctionExpression can be referenced from inside the FunctionExpression's FunctionBody to allow the function to call itself recursively. However, unlike in a FunctionDeclaration, the Identifier in a FunctionExpression cannot be referenced from and does not affect the scope enclosing the FunctionExpression.

请注意，直到版本 8 的 Internet Explorer 行为不正确，因为名称实际上在封闭变量环境中可见，并且它引用了实际函数的副本(请参阅 patrick dw'在下面评论).

Please note that Internet Explorer up to version 8 doesn't behave correctly as the name is actually visible in the enclosing variable environment, and it references a duplicate of the actual function (see patrick dw's comment below).

或者您可以使用 arguments.callee 引用当前函数:

Alternatively you could use arguments.callee to refer to the current function:

var factorial = function (n) {
    if (n <= 1) {
        return 1;
    }
    return n * arguments.callee(n-1);
}

ECMAScript 第 5 版禁止在 严格模式中使用 arguments.callee()，然而:

The 5th edition of ECMAScript forbids use of arguments.callee() in strict mode, however:

(来自 MDN):在普通代码中 arguments.callee 指的是封闭函数.这个用例很弱:只需命名封闭函数！此外，arguments.callee 大大阻碍了像内联函数这样的优化，因为如果访问 arguments.callee，必须能够提供对未内联函数的引用.严格模式函数的arguments.callee 是一个不可删除的属性，它在设置或检索时抛出.

(From MDN): In normal code arguments.callee refers to the enclosing function. This use case is weak: simply name the enclosing function! Moreover, arguments.callee substantially hinders optimizations like inlining functions, because it must be made possible to provide a reference to the un-inlined function if arguments.callee is accessed. arguments.callee for strict mode functions is a non-deletable property which throws when set or retrieved.

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