无穷大作为参数？

Question

我一直在通读 Underscore 库源代码，发现了这个：

  _.iteratee = builtinIteratee = function(value, context) {
    return cb(value, context, Infinity);
  };

参数Infinity是什么意思？

编辑：

抱歉，这里是 cb 和 optimizeCb。他们将回调转换为适当的迭代器。

  var optimizeCb = function(func, context, argCount) {
    if (context === void 0) return func;
    switch (argCount) {
      case 1: return function(value) {
        return func.call(context, value);
      };
      // The 2-parameter case has been omitted only because no current consumers
      // made use of it.
      case null:
      case 3: return function(value, index, collection) {
        return func.call(context, value, index, collection);
      };
      case 4: return function(accumulator, value, index, collection) {
        return func.call(context, accumulator, value, index, collection);
      };
    }
    return function() {
      return func.apply(context, arguments);
    };
  };

  // An internal function to generate callbacks that can be applied to each
  // element in a collection, returning the desired result — either `identity`,
  // an arbitrary callback, a property matcher, or a property accessor.
  var cb = function(value, context, argCount) {
    if (_.iteratee !== builtinIteratee) return _.iteratee(value, context);
    if (value == null) return _.identity;
    if (_.isFunction(value)) return optimizeCb(value, context, argCount);
    if (_.isObject(value) && !_.isArray(value)) return _.matcher(value);
    return _.property(value);
  };

Answer 1

这意味着参数在所有意图和目的上都大于所有其他数字：

来自MDN：

The initial value of Infinity is Number.POSITIVE_INFINITY. The value Infinity (positive infinity) is greater than any other number. Mathematically, this value behaves the same as infinity; for example, any positive number multiplied by Infinity equals Infinity, and any number divided by Infinity equals 0.

Answer 2

Infinity 被解释为数字。在这种情况下，源头在这里：

  // Internal function that returns an efficient (for current engines) version
  // of the passed-in callback, to be repeatedly applied in other Underscore
  // functions.
  var optimizeCb = function(func, context, argCount) {
    if (context === void 0) return func;
    switch (argCount == null ? 3 : argCount) {
      case 1: return function(value) {
        return func.call(context, value);
      };
      // The 2-argument case is omitted because we’re not using it.
      case 3: return function(value, index, collection) {
        return func.call(context, value, index, collection);
      };
      case 4: return function(accumulator, value, index, collection) {
        return func.call(context, accumulator, value, index, collection);
      };
    }
    return function() {
      return func.apply(context, arguments);
    };
  };

注意 Infinity 传递给了参数 argCount。 switch/case 语句将退出并 return 一个函数，该函数将简单地将上下文和参数应用到回调函数。使用 Infinity 似乎可以确保失败的情况。

无穷大作为参数？

Infinity as parameter?

javascript

underscore.js