Java中的File.rename（） - 它是一个原子操作吗？(File.rename() in Java - is it an atomic operation? [duplicate])

 您可以按如下方式转换数组： 
 
var userMap = userdata1.reduce(function(rv, v) {
  rv[v.id] = v;
  return rv;
}, {});
 
 这将为您提供一个将“id”值映射到原始对象的对象。 然后，您将访问如下值： 
 
var someUser = userMap[ someUserId ];
 
 此设置将比您的数组更有效，因为查找条目需要花费一定时间与“id”字符串本身的大小成比例（加上一点）。 在您的版本中，您必须搜索（平均）每个查找的一半列表。 对于一小组记录，差异将是不重要的，但如果你有数百或数千个记录，差异将是巨大的。 
 
 .reduce()函数在旧版浏览器中不可用， 但MDN文档站点上提供了一个填充补丁： 
 
// copied from MDN
if ('function' !== typeof Array.prototype.reduce) {
  Array.prototype.reduce = function(callback, opt_initialValue){
    'use strict';
    if (null === this || 'undefined' === typeof this) {
      // At the moment all modern browsers, that support strict mode, have
      // native implementation of Array.prototype.reduce. For instance, IE8
      // does not support strict mode, so this check is actually useless.
      throw new TypeError(
          'Array.prototype.reduce called on null or undefined');
    }
    if ('function' !== typeof callback) {
      throw new TypeError(callback + ' is not a function');
    }
    var index, value,
        length = this.length >>> 0,
        isValueSet = false;
    if (1 < arguments.length) {
      value = opt_initialValue;
      isValueSet = true;
    }
    for (index = 0; length > index; ++index) {
      if (this.hasOwnProperty(index)) {
        if (isValueSet) {
          value = callback(value, this[index], index, this);
        }
        else {
          value = this[index];
          isValueSet = true;
        }
      }
    }
    if (!isValueSet) {
      throw new TypeError('Reduce of empty array with no initial value');
    }
    return value;
  };
}

You can transform your array as follows:
 
var userMap = userdata1.reduce(function(rv, v) {
  rv[v.id] = v;
  return rv;
}, {});
 
That will give you an object that maps the "id" values onto the original object. You would then access the values like this:
 
var someUser = userMap[ someUserId ];
 
This set up will be much more efficient than your array, because finding an entry takes an amount of time proportional to the size of the "id" strings themselves (plus a little). In your version, you have to search through (on average) half the list for each lookup. For a small set of records, the difference would be unimportant, but if you've got hundreds or thousands of them the difference will be huge.
 
The .reduce() function is not available in older browsers, but there's a fill-in patch available on the MDN documentation site:
 
// copied from MDN
if ('function' !== typeof Array.prototype.reduce) {
  Array.prototype.reduce = function(callback, opt_initialValue){
    'use strict';
    if (null === this || 'undefined' === typeof this) {
      // At the moment all modern browsers, that support strict mode, have
      // native implementation of Array.prototype.reduce. For instance, IE8
      // does not support strict mode, so this check is actually useless.
      throw new TypeError(
          'Array.prototype.reduce called on null or undefined');
    }
    if ('function' !== typeof callback) {
      throw new TypeError(callback + ' is not a function');
    }
    var index, value,
        length = this.length >>> 0,
        isValueSet = false;
    if (1 < arguments.length) {
      value = opt_initialValue;
      isValueSet = true;
    }
    for (index = 0; length > index; ++index) {
      if (this.hasOwnProperty(index)) {
        if (isValueSet) {
          value = callback(value, this[index], index, this);
        }
        else {
          value = this[index];
          isValueSet = true;
        }
      }
    }
    if (!isValueSet) {
      throw new TypeError('Reduce of empty array with no initial value');
    }
    return value;
  };
}