JS go trough object and check if another object contains its value

Question

I'm trying to go trough JS object (1) to find out if value exists on another object (2) and return object (2) found value.

var returnObj = [];
    selectedValues.forEach(function(value, key){
        var found = valuesObject.some(function (el) {
            if (el.item_id === value){
                return el.item_id;
            }
        });
        console.log(found);
    });

in this case I can only find out if its exists or not by getting true/false and I've also tried this

var returnObj = [];
    selectedValues.forEach(function(value, key){
        console.log(_.intersection(valuesObject, value));
    });

but in this case it returns me only empty arrays instead of object (2) value which was found by object (1) value

Answer 1

If you do a return inside of an .forEach call, you will only return out of the callback you passed to the forEach function, not your enclosing function. You can use a standard for-loop, where you can return out of.

Assuming you have a list of "values" you want to find in the second object:

const values = [/*...*/];

Object.keys(secondObject).forEach(key => {
  const value = secondObject[key];

  if (values.includes(value)) {
    /* secondObject has a property with the values you are looking for */
  }
});

Object.keys gives you an array of property keys of an object. Depending on your environment you can also use Object.values(), this will return you an array of values (not keys) for a given object.

Answer 2

Just keep it simple and basic:

for (var i = 0; i < selectedValues.length; i++) {
    for (var j = 0; j < valuesObject.length; j++) {
        if (selectedValues[i] === valuesObject[j].item_id) {
            return valuesObject[j].item_id;
        }
    }
}

If you prefer one line:

return selectedValues.length && selectedValues.map(value => valuesObject.find(v => v.item_id === value))[0]

Answer 3

Perhaps I've got the setup wrong, but seeing returnObj is an array, filtering seems to be a good option. For example in combination with a Set:

let set = new Set(valuesObject.map(o=>o.item_id)),
    returnObj = selectedValues.filter(s=>set.has(s));

Example:

let selectedValues = ['aaa', 'bbb', 'ccc', 'ddd'],
	valuesObject = [ {item_id:'ddd'}, {item_id:'eee'}, {item_id:'bbb'}];


let set = new Set(valuesObject.map(o=>o.item_id)),
	returnObj = selectedValues.filter(s=>set.has(s));

console.log(returnObj);