javascript - 从对象数组中添加属性

Question

我正在尝试从对象数组中添加 ID 属性。显示的结果是 01395 - 相反，它应该是 27(因为这就是 13 + 9 + 5 等于的值)。

我相信代码正在连接 ID 属性，而不是添加它们的预期结果。

var collection = [{
  "Name": "Charlie",
  "ID": "13"
}, {
  "Name": "Emma",
  "ID": "9"
}, {
  "Name": "Bob",
  "ID": "5"
}];

total = 0, //set a variable that holds our total
  id = collection, //reference the element in the "JSON" aka object literal we want
  i = 0;
for (i = 0; i < id.length; i++) { //loop through the array
  total += id[i].ID; //Do the math!
}
console.log(total); //display the result

JsFiddle:https://jsfiddle.net/3r8vhfb2/

Answer 1

将其转换为Number

Unary plus (+), The unary plus operator precedes its operand and evaluates to its operand but attempts to converts it into a number, if it isn't already.

var collection = [{
  "Name": "Charlie",
  "ID": "13"
}, {
  "Name": "Emma",
  "ID": "9"
}, {
  "Name": "Bob",
  "ID": "5"
}];

var total = 0,
  id = collection;
for (var i = 0; i < id.length; i++) {
  total += +id[i].ID;
  //OR total += Number(id[i].ID);
}
console.log(total);

或使用 Array#reduce <强>:

var collection = [{
  "Name": "Charlie",
  "ID": "13"
}, {
  "Name": "Emma",
  "ID": "9"
}, {
  "Name": "Bob",
  "ID": "5"
}];

var total = collection.reduce(function(a, b) {
  return +(a.ID || a) + +(b.ID);
});
console.log(total);