如何从javascript中的对象数组中获取键值的总和？

Question

I need to sum all of the values of a key "number" from several objects within an array. What would be the correct way to do this? This is what I've tried.

var numarray = [{"number":"10"},{"number":"2"},{"number":"5"},
{"number":"3"},{"number":"21"},{"number":"43"},{"number":"30"}];

function Sum() {
  var sum;

  for (number in numarray[i]){
    alert(sum); //sum would be the result I need to get
  }
}

Answer 1

Use forEach to loop through each of the json object.

Use parseInt to convert the values to integer

var numarray = [
{"number":"10"},
{"number":"2"},
{"number":"5"},
{"number":"3"},
{"number":"21"},
{"number":"43"},
{"number":"30"}];

function Sum(){
var sum=0;

numarray.forEach(function(item){
 sum += parseInt(item.number)
})
document.write('<pre>'+sum+'</pre>')
}
Sum()

DEMO

EDIT

When using parseInt it is better to specify the radix

parseInt(item.number,10)

Using a 10 radix means the number is parsed with a base 10 and thus turns the number into the integer .If parseInt detects a leading zero it will parse the number in octal base

Using Number

Number(item.number)

It will not detect any any octal

Answer 2

You can use reduce for this:

Here's how you would normally find the sum of elements in an array:

var sum = arr.reduce(function(a,b) {
  return a + b;
});

Since you have an array of objects, you'll need to change this to something like:

var sum = arr.reduce(function(a,b) {
  return parseFloat(a) + parseFloat(b.number);
}, 0);

Notice the 0 I've added added as a parameter? It's the default parameter and required in this case.