检查 TypeScript 对象中的属性是否为空

Question

I have an object that looks like this:

protected products: {
  color: string[],
  brand: number[],
} = {};

I want to check if the properties of products are null (simply Array(0) ). How can I do it?

I am using "target": "es2015".

Answer 1

You could probably use lodash _.isEmpty(value) :

_.isEmpty(null);
// => true

_.isEmpty(true);
// => true

_.isEmpty(1);
// => true

_.isEmpty([1, 2, 3]);
// => false

_.isEmpty({ 'a': 1 });
// => false

Answer 2

Could try this:

const checkEmptyObj = (object) => {
  // gets an array of the values for each kv pair in your object
  const values =  Object.values(object);

  // if you add kv pairs with non array types, will have to adjust this
  // removes all zero length arrays (or strings) from values array
  const nonEmptyValues = values.filter(value => value.length > 0)

  // if any items are in the nonEmptyValues array, return false
  return nonEmptyValues.length < 1
}

This is not a catch all solution, it needs more work for use beyond your stated case. Specifically, it only works on objects of one level deep. If you are passing in a nested object, you'll have to adjust the function to be recursive. If you expect to have other data types, you will have to do some handling of those inside the filter function (the .length call will fail on numbers and objects, among others).

After more thought, I like this solution more.

return values.every(value => value.length === 0)

Answer 3

For checking if all the arrays are empty, you can approach it as follow:

This is assuming that all values are arrays

 let products = {color: [],brand: []}; let allEmpty = Object.values(products).every(({length}) => !Boolean(length)); console.log(allEmpty);

As the argument is an array, we can use the destructuring assignment as follow:

{length} // Basically to extract the attribute length

The number 0 is considered falsy , so we can do explicit type coercion (or type casting) on values as follow:

!Boolean(length) // Coerce to boolean the number from arr.length
                 // The negation is needed because if the length === 0 that 
                 // means the array is empty, so we want the result 
                 // as true in our handler for the function every