从外部函数（数组）理解返回函数（x）

Question

我正在学习JavaScript，并对以下练习感到困惑。我不得不创建一个过滤器，接受另一个函数作为排序方法。我无法理解的是/usr/lib/jvm/java-8-oracle/bin/java -agentlib:jdwp=transport=dt_socket,address=127.0.0.1:47427,suspend=y,server=n -Dfile.encoding=UTF-8 -classpath /usr/lib/jvm/java-8-oracle/jre/lib/charsets.jar:/usr/lib/jvm/java-8-oracle/jre/lib/deploy.jar:/usr/lib/jvm/java-8-oracle/jre/lib/ext/cldrdata.jar:/usr/lib/jvm/java-8-oracle/jre/lib/ext/dnsns.jar:/usr/lib/jvm/java-8-oracle/jre/lib/ext/jaccess.jar:/usr/lib/jvm/java-8-oracle/jre/lib/ext/jfxrt.jar:/usr/lib/jvm/java-8-oracle/jre/lib/ext/localedata.jar:/usr/lib/jvm/java-8-oracle/jre/lib/ext/nashorn.jar:/usr/lib/jvm/java-8-oracle/jre/lib/ext/sunec.jar:/usr/lib/jvm/java-8-oracle/jre/lib/ext/sunjce_provider.jar:/usr/lib/jvm/java-8-oracle/jre/lib/ext/sunpkcs11.jar:/usr/lib/jvm/java-8-oracle/jre/lib/ext/zipfs.jar:/usr/lib/jvm/java-8-oracle/jre/lib/javaws.jar:/usr/lib/jvm/java-8-oracle/jre/lib/jce.jar:/usr/lib/jvm/java-8-oracle/jre/lib/jfr.jar:/usr/lib/jvm/java-8-oracle/jre/lib/jfxswt.jar:/usr/lib/jvm/java-8-oracle/jre/lib/jsse.jar:/usr/lib/jvm/java-8-oracle/jre/lib/management-agent.jar:/usr/lib/jvm/java-8-oracle/jre/lib/plugin.jar:/usr/lib/jvm/java-8-oracle/jre/lib/resources.jar:/usr/lib/jvm/java-8-oracle/jre/lib/rt.jar:/home/hhrutz/Documents/devel/Wolkenpumpe/target/scala-2.11/test-classes:/home/hhrutz/Documents/devel/Wolkenpumpe/target/scala-2.11/classes:/home/hhrutz/.ivy2/cache/com.github.scopt/scopt_2.11/jars/scopt_2.11-3.4.0.jar:/home/hhrutz/.ivy2/cache/org.slf4j/slf4j-simple/jars/slf4j-simple-1.7.18.jar:/home/hhrutz/.ivy2/cache/org.slf4j/slf4j-api/jars/slf4j-api-1.7.18.jar:/home/hhrutz/.ivy2/cache/org.scalatest/scalatest_2.11/bundles/scalatest_2.11-2.2.6.jar:/home/hhrutz/.ivy2/cache/org.scala-stm/scala-stm_2.11/jars/scala-stm_2.11-0.7.jar:/home/hhrutz/.ivy2/cache/org.scala-lang.modules/scala-xml_2.11/bundles/scala-xml_2.11-1.0.5.jar:/home/hhrutz/.ivy2/cache/org.scala-lang.modules/scala-swing_2.11/bundles/scala-swing_2.11-1.0.2.jar:/home/hhrutz/.ivy2/cache/org.scala-lang/scala-reflect/jars/scala-reflect-2.11.7.jar:/home/hhrutz/.ivy2/cache/org.scala-lang/scala-library/jars/scala-library-2.11.8.jar:/home/hhrutz/.ivy2/cache/net.sourceforge.jtransforms/jtransforms/jars/jtransforms-2.4.0.jar:/home/hhrutz/.ivy2/cache/net.htmlparser.jericho/jericho-html/jars/jericho-html-3.3.jar:/home/hhrutz/.ivy2/cache/lucene/lucene/jars/lucene-1.4.3.jar:/home/hhrutz/.ivy2/cache/junit/junit/jars/junit-4.8.2.jar:/home/hhrutz/.ivy2/local/de.sciss/weblaf-ui/2.1.0/jars/weblaf-ui.jar:/home/hhrutz/.ivy2/local/de.sciss/weblaf-core/2.1.0/jars/weblaf-core.jar:/home/hhrutz/.ivy2/local/de.sciss/treetable-scala_2.11/1.3.8/jars/treetable-scala_2.11.jar:/home/hhrutz/.ivy2/local/de.sciss/treetable-java/1.3.8/jars/treetable-java.jar:/home/hhrutz/.ivy2/cache/de.sciss/topology_2.11/jars/topology_2.11-1.0.0.jar:/home/hhrutz/.ivy2/local/de.sciss/swingplus_2.11/0.2.1/jars/swingplus_2.11.jar:/home/hhrutz/.ivy2/local/de.sciss/submin/0.2.0/jars/submin.jar:/home/hhrutz/.ivy2/cache/de.sciss/span_2.11/jars/span_2.11-1.3.1.jar:/home/hhrutz/.ivy2/local/de.sciss/soundprocesses-views_2.11/3.4.0/jars/soundprocesses-views_2.11.jar:/home/hhrutz/.ivy2/local/de.sciss/soundprocesses-core_2.11/3.4.0/jars/soundprocesses-core_2.11.jar:/home/hhrutz/.ivy2/cache/de.sciss/serial_2.11/jars/serial_2.11-1.0.2.jar:/home/hhrutz/.ivy2/cache/de.sciss/scissdsp_2.11/jars/scissdsp_2.11-1.2.2.jar:/home/hhrutz/.ivy2/local/de.sciss/scalaosc_2.11/1.1.5/jars/scalaosc_2.11.jar:/home/hhrutz/.ivy2/local/de.sciss/scalacolliderugens-plugins_2.11/1.14.1/jars/scalacolliderugens-plugins_2.11.jar:/home/hhrutz/.ivy2/local/de.sciss/scalacolliderugens-core_2.11/1.14.1/jars/scalacolliderugens-core_2.11.jar:/home/hhrutz/.ivy2/local/de.sciss/scalacolliderugens-api_2.11/1.14.1/jars/scalacolliderugens-api_2.11.jar:/home/hhrutz/.ivy2/local/de.sciss/scalacolliderswing-core_2.11/1.28.0/jars/scalacolliderswing-core_2.11.jar:/home/hhrutz/.ivy2/local/de.sciss/scalacollider_2.11/1.18.1/jars/scalacollider_2.11.jar:/home/hhrutz/.ivy2/cache/de.sciss/scalaaudiofile_2.11/jars/scalaaudiofile_2.11-1.4.5.jar:/home/hhrutz/.ivy2/local/de.sciss/raphael-icons_2.11/1.0.3/jars/raphael-icons_2.11.jar:/home/hhrutz/.ivy2/cache/de.sciss/processor_2.11/jars/processor_2.11-0.4.0.jar:/home/hhrutz/.ivy2/local/de.sciss/prefuse-core/1.0.1/jars/prefuse-core.jar:/home/hhrutz/.ivy2/cache/de.sciss/numbers_2.11/jars/numbers_2.11-0.1.1.jar:/home/hhrutz/.ivy2/cache/de.sciss/model_2.11/jars/model_2.11-0.3.2.jar:/home/hhrutz/.ivy2/local/de.sciss/lucresynth_2.11/3.4.0/jars/lucresynth_2.11.jar:/home/hhrutz/.ivy2/local/de.sciss/lucreswing_2.11/1.3.0/jars/lucreswing_2.11.jar:/home/hhrutz/.ivy2/local/de.sciss/lucre-expr_2.11/3.3.1/jars/lucre-expr_2.11.jar:/home/hhrutz/.ivy2/local/de.sciss/lucre-core_2.11/3.3.1/jars/lucre-core_2.11.jar:/home/hhrutz/.ivy2/local/de.sciss/lucre-confluent_2.11/3.3.1/jars/lucre-confluent_2.11.jar:/home/hhrutz/.ivy2/local/de.sciss/lucre-bdb_2.11/3.3.1/jars/lucre-bdb_2.11.jar:/home/hhrutz/.ivy2/cache/de.sciss/intensitypalette/jars/intensitypalette-1.0.0.jar:/home/hhrutz/.ivy2/cache/de.sciss/fingertree_2.11/jars/fingertree_2.11-1.5.2.jar:/home/hhrutz/.ivy2/cache/de.sciss/fileutil_2.11/jars/fileutil_2.11-1.1.1.jar:/home/hhrutz/.iv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de.sciss.nuages.Demo 如何将for loop传递给value。你能解释一下吗？

x

Answer 1

您的过滤器函数接受要过滤的数组，以及执行过滤的函数。在这部分：

for (var i = 0; i < arr.length; i++) {

    var value = arr[i];
    if (func(value)) { //here, you invoke the function on the array's values
        result.push(value);
    }
}

因此，例如，如果我们查看inBetween(3, 6)函数，那就是：

return function(x) {
    return 3 <= x && x <= 6;
}

（如果您不理解这部分内容，请阅读更多有关Closures）

的内容

现在，该函数只是一个函数，它接受一个值，并返回true / false，判断它是否在3＆amp; 3之间。 6。

最终使用上述函数对每个数组的值（1,2,3 ... 7）进行调用。

您列出的所有其他功能也是如此。

Answer 2

我将以此行为例：

filter(arr, inArray([1, 2, 10])) );

使用arr = [1, 2, 10]调用

inArray 。

它为特定的 arr 返回以下（匿名）函数：

function (x) {
    return arr.indexOf(x) != -1;
}

所以原来的行现在可以被描绘成：

filter(arr, function (x) {
    return [1, 2, 10].indexOf(x) != -1;
});

现在调用过滤器并将 func 设置为该匿名函数。以下代码调用该函数：

    if (func(value)) {
        result.push(value);
    }

因此，当调用 func 时，这实际上意味着调用上述匿名函数，并且参数 x 被设置为 value at通话的那一刻。它与任何其他函数调用一样，函数的参数获取实际调用中参数的值。

Answer 3

在这一行：

filter(arr, inBetween(3, 6))

您不是“传递函数”，而是传递函数调用的结果。结果是另一个（匿名/未命名）函数。

从这一行：

function filter(arr, func) {

我们知道作为filter的参数传递的函数的名称是func，然后是：

if (func(value)) {

执行此功能。

在JavaScript中，函数只是一个像其他对象一样的对象。要区分“函数对象引用”和“函数调用”，可以查找()。

inBetween是一个函数对象引用，inBetween(x, y)表示调用此函数。

可以定义匿名函数，将其分配给变量，也可以作为参数传递。它也可以在定义后立即执行：

function() {
  alert("called!");
}();

对于刚接触JavaScript的人来说，这可能看起来很奇特。