Let's consider an array:
arr = [{}, {}, {}, {}]
If we want to determine the length of the array by counting only objects that contain at least one property, we can do this:
[{}, {name: "Manchester United", odds: 3}, {}, {}] // 1
[{}, {name: "Liverpool", odds: 1}, {name: "Chelsea", odds: 2} ,{}] // 2
Is there a way to achieve this goal?
arr.filter(x => Object.keys(x).length).length
Another way to understand the code above is that the Object.keys() function returns the names of properties from a given object. The first .length filters only items with at least one property, while the second .length counts how many objects meet this criteria.
UPDATE:
In the [].filter() method, it takes a function that results in a true or false value. Any number greater than 0 is considered as true, which is equivalent to .length !== 0.
The assumption made here is that every element in the array is non-null. With this assumption, checking for null values inside the [].filter() doesn't make sense. In TypeScript, this provides a static check for the variable arr. If this assumption is incorrect and there are null values present, an error will be thrown, something that I prefer as it helps uncover issues. Runtime errors are not hidden in my code, and if there are any, I will reassess the underlying assumption. However, I don't think that's the case here.
If you run the following code:
arr.map(x=> Object.keys(x).length)
you will receive:
[ 0, 0, 0, 1 ]
When an object is empty, it has no keys and therefore its length is 0.
To obtain a true/false result, use the following code:
arr.map(x=> Object.keys(x).length).some(x=>x>0)
console.log("[{},{}]", [{},{}].map(x=> Object.keys(x).length).some(x=>x>0))
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