Combine two objects in an array to new object?

Question

I'm working on a script where I'm converting a text file "data" to an array of objects and will subsequently join that array to Geojson via a common key "GEOID". In "data" I have two objects STATE_FIP and COUNTY_FIP. Those two combined will create a common key to match "GEOID". I need to concatenate them programmatically. Is there a way to do this easily? Below is a screen shot of "data" Thank you!

Answer 1

Not much info given but...try this:

var additionalProps = {}

data.forEach(obj => {
    geoid = obj.STATE_FIP + obj.COUNTY_FIP
    additionalProps[geoid] = obj
})

var updatedGeoJson = {
    "type": "FeatureCollection",
    "features": []
  };

oldGeoJson.features.forEach(x => {
    geoid = x.properties.GEOID 
    newProps = {...x.properties, ...additionalProps[geoid]}
    x.properties = newProps
    updatedGeoJson.features.push(x)
})