Java中一元+的作用是什么? [英] What is unary + used for in Javascript?

问题描述

我从 Underscore.js

  _.map = _.collect = function(obj, iterator, context) {
    var results = [];
    if (obj == null) return results;
    if (nativeMap && obj.map === nativeMap) return obj.map(iterator, context);
    each(obj, function(value, index, list) {
      results[results.length] = iterator.call(context, value, index, list);
    });
    if (obj.length === +obj.length) results.length = obj.length;
    return results;
  };

我想知道if (obj.length === +obj.length)是什么?

推荐答案

+length是一种将任何内容转换为数字的方法.

+length is a method to convert anything to a number.

如果是数字，则值不变，并且比较返回true.
如果不是数字，则断言为假.

If it's a number, the value doesn't change, and the comparison returns true.
If it's not a number, the assertion is false.

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