我有这样的东西:
$scope.traveler = [
{ description: 'Senior', Amount: 50},
{ description: 'Senior', Amount: 50},
{ description: 'Adult', Amount: 75},
{ description: 'Child', Amount: 35},
{ description: 'Infant', Amount: 25 },
];
现在要得到这个数组的总量，我做了这样的事情:
$scope.totalAmount = function(){
var total = 0;
for (var i = 0; i < $scope.traveler.length; i++) {
total = total + $scope.traveler[i].Amount;
}
return total;
}
当只有一个数组时这很容易，但是我有其他数组具有不同的属性名，我想求和。
如果我能做这样的事，我会更高兴:
$scope.traveler.Sum({ Amount });
但我不知道如何在将来重复使用它，就像这样:
$scope.someArray.Sum({ someProperty });
回答
我决定使用@gruff-bunny建议，这样我就避免了原生对象（数组）的原型化
我只是对他的回答做了一点修改，验证数组和要求和的值不为空，这是我的最终实现:
$scope.sum = function (items, prop) {
if (items == null) {
return 0;
}
return items.reduce(function (a, b) {
return b[prop] == null ? a : a + b[prop];
}, 0);
};
更新的答案
由于在数组原型中添加函数的所有缺点，我正在更新这个答案，以提供一个备选方案，使语法保持与问题中最初要求的语法相似。
class TravellerCollection extends Array {
sum(key) {
return this.reduce((a, b) => a + (b[key] || 0), 0);
}
}
const traveler = new TravellerCollection(...[
{ description: 'Senior', Amount: 50},
{ description: 'Senior', Amount: 50},
{ description: 'Adult', Amount: 75},
{ description: 'Child', Amount: 35},
{ description: 'Infant', Amount: 25 },
]);
console.log(traveler.sum('Amount')); //~> 235
原始答案
由于它是一个数组，您可以向数组原型添加一个函数。
traveler = [
{ description: 'Senior', Amount: 50},
{ description: 'Senior', Amount: 50},
{ description: 'Adult', Amount: 75},
{ description: 'Child', Amount: 35},
{ description: 'Infant', Amount: 25 },
];
Array.prototype.sum = function (prop) {
var total = 0
for ( var i = 0, _len = this.length; i < _len; i++ ) {
total += this[i][prop]
}
return total
}
console.log(traveler.sum("Amount"))
小提琴:http://jsfiddle.net/9bamj/
我知道这个问题有一个公认的答案，但我想我应该加入一个使用array.Reduce的备选方案，因为求和一个数组是Reduce的规范示例:
$scope.sum = function(items, prop){
return items.reduce( function(a, b){
return a + b[prop];
}, 0);
};
$scope.travelerTotal = $scope.sum($scope.traveler, 'Amount');
小提琴
再看一下，这就是本机JavaScript函数Map和Reduce的构建目的（Map和Reduce是许多语言中的强大功能）。
var traveler = [{description: 'Senior', Amount: 50},
{description: 'Senior', Amount: 50},
{description: 'Adult', Amount: 75},
{description: 'Child', Amount: 35},
{description: 'Infant', Amount: 25}];
function amount(item){
return item.Amount;
}
function sum(prev, next){
return prev + next;
}
traveler.map(amount).reduce(sum);
// => 235;
// or use arrow functions
traveler.map(item => item.Amount).reduce((prev, next) => prev + next);
注意:通过制作单独的较小函数，我们获得了再次使用它们的能力。
// Example of reuse.
// Get only Amounts greater than 0;
// Also, while using Javascript, stick with camelCase.
// If you do decide to go against the standards,
// then maintain your decision with all keys as in...
// { description: 'Senior', Amount: 50 }
// would be
// { Description: 'Senior', Amount: 50 };
var travelers = [{description: 'Senior', amount: 50},
{description: 'Senior', amount: 50},
{description: 'Adult', amount: 75},
{description: 'Child', amount: 35},
{description: 'Infant', amount: 0 }];
// Directly above Travelers array I changed "Amount" to "amount" to match standards.
function amount(item){
return item.amount;
}
travelers.filter(amount);
// => [{description: 'Senior', amount: 50},
// {description: 'Senior', amount: 50},
// {description: 'Adult', amount: 75},
// {description: 'Child', amount: 35}];
// Does not include "Infant" as 0 is falsey.
