从数组中的对象中的数组中获取字符串值

Question

I have the following JSON object:

 var test = { data: [{ itemID: 0, categories: [{ id: 0, type: 'a', name: 'world' }, { id: 1, type: 'b', name: 'plants' }] }, { itemID: 1, categories: [{ id: 2, type: 'w', name: 'cars' }, { id: 3, type: 't', name: 'bicycles' }] } ] }; console.log([].concat .apply([], test.data.map(item => item.categories.map(el => el.type)))); 

What I want to do is, to get all types in an array. So the result should look like this:

['a', 'b', 'w', 't']

What I did:

[].concat
.apply([],  test.data.map(item => item.categories.map(el => el.type)))

I have the feeling that this could be done easier.

Does someone know a better solution ?

Answer 1

You can use Array.prototype.map() and Array.prototype.flat() :

The flat() method creates a new array with all sub-array elements concatenated into it recursively up to the specified depth.

Where depth is Optional

The depth level specifying how deep a nested array structure should be flattened. Defaults to 1.

 var test = { data: [{ itemID: 0, categories: [{ id: 0, type: 'a', name: 'world' }, { id: 1, type: 'b', name: 'plants' }] }, { itemID: 1, categories: [{ id: 2, type: 'w', name: 'cars' }, { id: 3, type: 't', name: 'bicycles' }] } ] }; var type = test.data.map(item => item.categories.map(el => el.type)).flat(); console.log(type); 

Answer 2

Use Array.reduce

 var test = {data: [{itemID: 0,categories: [{id: 0,type: 'a',name: 'world'}, {id: 1,type: 'b',name: 'plants'}]},{itemID: 1,categories: [{id: 2,type: 'w',name: 'cars'}, {id: 3,type: 't',name: 'bicycles'}]}]}; let result = test.data.reduce((a,c) => a.concat(c.categories.map(v => v.type)), []); console.log(result);