如何遍历特定索引并检查javascript / angular中的值

Question

I have the following model in my angular app:

members = [
            {
                id: 'member1',
                name: '',
                instrument1: '',
                instrument2: ''
            },...
            ]

I would like to generate a filtered array that can be accessed with an ng-repeat. the filtered array would contain indexes for all instruments that have values not equal to "" or null. really the contents of the array are not important for the immediate term, it could just be [0,1,2....].

Answer 1

I suggest you filter the members and get the length:

function hasAnInstrument(member) {
  // return true if you want to count the member, for instance:
  return !!member.instrument1 || !!member.instrument2;
}

var counter = members.filter(hasAnInstrument).length;

Answer 2

EDITED ANSWER

var a = [
  {instrument1: true, instrument2: false},
  {instrument1: false, instrument2: false},
  {instrument1: true, instrument2: true}
];

var count = a.map(function(m) {
  return +!!m.instrument1 + +!!m.instrument2
}).reduce(function(a, b) {
  return a + b
}, 0);

console.log(count);

The map transforms each element into 0, 1 or 2 regarding of the properties converted into Booleans, and the reduce simply adds the individual counters together.

Notes

• !!something converts something into a Boolean. +something converts something into a Number, and true is converted into 1 while false is converted into 0 . Pretty convenient.

• This code relies on the fact that empty strings or null , when converted to a Boolean, equal false . This is a pretty weak thing to rely on for models, and in a production/enterprise environment, I'd suggest to make this more explicit by adding a step where the data gets sanitized.

• The code above is so concise it's almost obfuscated. In a production/enterprise environment, I'd suggest loosen it a little bit so it's more explicit.