Extend object. Is there any way to assign values when the property is available?

Question

I have an object

        var general = {
            'primary_color': {'value': undefined},
            'logo': {'value': undefined},
        },

When i receive data from server i receive something like this

        var response = {
            'primary_color': {'value': '#DDD'},
            'logo': null,
        },

I wonder if there is any one liner function using will convert my structure as

        var result = {
            'primary_color': {'value': '#DDD'},
            'logo': {'value': undefined},
        },

Answer 1

You can do this with _.mergeWith() by defining which value should be returned, when the current value is null or undefined by using _.isNil():

var general = { 'primary_color': {'value': undefined}, 'logo': {'value': undefined} };
var response = { 'primary_color': {'value': '#DDD'}, 'logo': null };

var result = _.mergeWith({}, general, response, function(objValue, srcValue) {
  if(_.isNil(objValue)) {
    return srcValue;
  }
  
  if(_.isNil(srcValue)) {
    return objValue;
  }
});

console.log(result);

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