use filter to return property values in an object

Question

Trying to make a function that uses filter but not a for or while loop or foreach function, that will loop through an array of objects only to return their property values.

Answer 1

Use .filter when you want to get the whole object(s) that match the expected property or properties. Use .map when you have an array of things and want to do some operation on those things and get the result.

The challenge is to get all of the messages that are 50 characters or less. So you can use filter to get only the messages that pass that test and then map to get only the message text.

function getShortMessages(messages) {
  return messages
    .filter(function(obj) {
      return obj.message.length <= 50;
    })
    .map(function(obj) {
      return obj.message;
    });
}

JSFiddle: http://jsfiddle.net/rbbk65sq/

If it is possible for the input objects to not have a message property, you would want to test for it with obj.message && obj.message.length <= 50 like this:

function getShortMessages(messages) {
  return messages
    .filter(function(obj) {
      return obj.message && obj.message.length <= 50;
    })
    .map(function(obj) {
      return obj.message;
    });
}

ES6

The same code samples in ES6:

const getShortMessages = (messages) => messages
  .filter(obj => obj.message.length <= 50)
  .map(obj => obj.message);

And if the input objects might not have the message property:

const getShortMessages = (messages) => messages
  .filter(obj => obj.message && obj.message.length <= 50)
  .map(obj => obj.message);

JSFiddle: http://jsfiddle.net/npfsrwjq/