Javascript 使用带有一个附加参数的函数的 map() 的 JS 回调
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JS callback using map() with a function that has one additional parameter
提问by syntaxerror
I'm trying to find a way to use JS's Array.prototype.map()functionality with a function that has one additional parameter more (if possible at all, and I'd like to avoidhaving to rewrite built-in Array.prototype.map()).
This documentation is very good, but does not cover the "one-or-more-additional-parameter" case:
我试图找到一种方法来使用 JS 的Array.prototype.map()功能，该函数还有一个额外的参数（如果可能的话，我想避免重写 built-in Array.prototype.map()）。这个文档非常好，但不包括“一个或多个附加参数”的情况：
https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Array/map
https://developer.mozilla.org/en/JavaScript/Reference/Global_Objects/Array/map
function doOpSingle(elem)
{
// do something with one array element
}
var A = ["one", "two", "three", "four"];
var x = A.map(doOpSingle); // this will execute doOpSingle() on each array element
So far, so good. But what if the function in question has twoparameters, like e. g. a flag you might want to OR to it (think of bit masks)
到现在为止还挺好。但是如果有问题的函数有两个参数，比如一个你可能想要对其进行 OR 的标志（想想位掩码）怎么办
function doOpSingle2(arrelem,flag)
{
// do something with one array element
}
var A = ["one", "two", "three", "four"];
var theFlag = util.getMask(); // call external function
var y = A.map(doOpSingle2(theFlag)); // this does not work!
Any solutions should do withoutforloops, of course, because that's why we have map(), to make our code cleaner w/getting rid of these!
当然，任何解决方案都应该没有for循环，因为这就是为什么我们有map(), 使我们的代码更干净，并且摆脱这些！
回答by Niet the Dark Absol
Use an anonymous function:
使用匿名函数：
A.map(function(a) {return doOpSingle2(a,theFlag);});
回答by Esailija
A.map(doOpSingle2.bind(null, theFlag))
A.map(doOpSingle2.bind(null, theFlag))
theFlagwill be first argument though:
theFlag不过将是第一个参数：
function doOpSingle2( flag, elem ) { ... }
function doOpSingle2( flag, elem ) { ... }
回答by MatrixFrog
Edit: Nevermind, you don't really need Closure for this. See Esailija's answer.
编辑：没关系，你真的不需要闭包。请参阅 Esailja 的回答。
There is another option, if you happen to be using the Closure library. First you have to rewrite doOpSingle2 so that the flag is first:
如果您碰巧使用Closure 库，还有另一种选择。首先你必须重写 doOpSingle2 以便标志是第一个：
function doOpSingle2(flag, arrelem)
{
// do something with one array element
}
then you can do
那么你可以做
var y = A.map(goog.partial(doOpSingle2, theFlag));
goog.partial partially appliesthe function, so goog.partial(doOpSingle2, theFlag)is equivalent to this function:
goog.partial部分应用了这个函数，所以goog.partial(doOpSingle2, theFlag)等价于这个函数：
function(arrElem) {
return doOpSingle2(theFlag, arrElem);
}
In this particular case, I probably wouldn't recommend this approach, but there might be similar situations where it works well.
在这种特殊情况下，我可能不会推荐这种方法，但可能有类似的情况下它运行良好。
回答by UltraInstinct
Use an anonymous function.
使用匿名函数。
var y = A.map(function(x){doOpSingle2(x,theFlag);});
