What is the best way to loop through this array of objects?

Question

I have an array of objects like this:

const opts_timeline = [
      {
        type: {...},
        stimulus: ''
      },
      {
        type: {...},
        stimulus: ''
      },
      {
        timeline: [{type: {...}, stimulus: ''}],
        timeline_variable: [{...}, {...}]
      },
      {
        type: {...},
        stimulus: ''
      },
    ]

The type object inside it is like this:

type: {
  info: {name: '', preloads: ''},
  stimulus: ''
}

I want to loop through this array and retrieve some properties inside type objects, I tried the forEach method:

opts_timeline.forEach(multiple_trials => {
      if (!multiple_trials.hasOwnProperty('type')) {
        multiple_trials.timeline.forEach(trial => {
          var preloads = trial.type.info.preloads;
          if (typeof preloads !== 'undefined') {
            for (var i = 0; i < preloads.length; i++) {
              var type = trial.type.info.name;
              var param = preloads[i].parameter;
              var media = preloads[i].media_type;
              var func = preloads[i].conditional_function;
              var trials = timeline.trialsOfType(type);
              // ...
            }
          }
        })
      } else {
        var preloads = multiple_trials.type.info.preloads;
        if (typeof preloads !== 'undefined') {
          for (var i = 0; i < preloads.length; i++) {
            var type = multiple_trials.type.info.name;
            var param = preloads[i].parameter;
            var media = preloads[i].media_type;
            var func = preloads[i].conditional_function;
            var trials = timeline.trialsOfType(type);
            // ...
          }
        }
      }
    });

But this code seems redundant. Is there anyway to optimize it, or separate some of them into a helper function? Thanks!

The usual way to get rid of duplicate code is putting it into a named function. Wouldn't that work here? — Barmar
– Barmar, Commented Apr 16, 2020 at 20:56

bryan60 · Accepted Answer · 2020-04-16 21:03:46Z

1

seems like you can simplify this like:

  opts_timeline.forEach(multiple_trials => {
    (multiple_trials.timeline || [multiple_trials]).forEach(trial => {
      var preloads = trial.type.info.preloads;
      if (typeof preloads !== 'undefined') {
        for (var i = 0; i < preloads.length; i++) {
          var type = trial.type.info.name;
          var param = preloads[i].parameter;
          var media = preloads[i].media_type;
          var func = preloads[i].conditional_function;
          var trials = timeline.trialsOfType(type);
          // ...
        }
      }
    })
  });

if there's a timeline, iterate that, otherwise, wrap the trial in an array and iterate that.

answered Apr 16, 2020 at 21:03

bryan60

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