为什么Array .filter方法返回一个空数组？

Question

The below is really confusing me, I am trying to filter the musicData array to only have contents where the artist + name length are less than 25. I have logged out through the iterations etc. and everything looks good, so i'm completely stumped why it returns an empty array.

Any help would be much appreciated.

const musicData = [
    { artist: 'Adele', name: '25', sales: 1731000 },
    { artist: 'Drake', name: 'Views', sales: 1608000 },
    { artist: 'Beyonce', name: 'Lemonade', sales: 1554000 },
    { artist: 'Chris Stapleton', name: 'Traveller', sales: 1085000 },
    { artist: 'Pentatonix', name: 'A Pentatonix Christmas', sales: 904000 },
    { artist: 'Original Broadway Cast Recording', name: 'Hamilton: An American Musical', sales: 820000 },
    { artist: 'Twenty One Pilots', name: 'Blurryface', sales: 738000 },
    { artist: 'Prince', name: 'The Very Best of Prince', sales: 668000 },
    { artist: 'Rihanna', name: 'Anti', sales: 603000 },
    { artist: 'Justin Bieber', name: 'Purpose', sales: 554000 }
];

var totalAlbumSales=musicData.filter((curr) => {
    curr.artist.length+curr.name.length <25
})

Answer 1

You forgot the return keyword to indicate what should be returned to the new array. Without that, you are just executing a statement.

Since your logic to determine what should be in the filtered array could easily be comprised of many statements, the return keyword is needed to explicitly indicate what goes in the result.

See documentation on Array.filter()

 const musicData = [ { artist: 'Adele', name: '25', sales: 1731000 }, { artist: 'Drake', name: 'Views', sales: 1608000 }, { artist: 'Beyonce', name: 'Lemonade', sales: 1554000 }, { artist: 'Chris Stapleton', name: 'Traveller', sales: 1085000 }, { artist: 'Pentatonix', name: 'A Pentatonix Christmas', sales: 904000 }, { artist: 'Original Broadway Cast Recording', name: 'Hamilton: An American Musical', sales: 820000 }, { artist: 'Twenty One Pilots', name: 'Blurryface', sales: 738000 }, { artist: 'Prince', name: 'The Very Best of Prince', sales: 668000 }, { artist: 'Rihanna', name: 'Anti', sales: 603000 }, { artist: 'Justin Bieber', name: 'Purpose', sales: 554000 } ]; var totalAlbumSales=musicData.filter((curr) => { return curr.artist.length + curr.name.length < 25 }) console.log(totalAlbumSales); 

Answer 2

You are missing the return keyword to make it a statement.

If you want to write that callback without a return then simply remove your brackets.

From MDN docs :

(param1, param2, …, paramN) => { statements }

(param1, param2, …, paramN) => expression

// equivalent to: => { return expression; }

Demo

 const musicData = [ { artist: 'Adele', name: '25', sales: 1731000 }, { artist: 'Drake', name: 'Views', sales: 1608000 }, { artist: 'Beyonce', name: 'Lemonade', sales: 1554000 }, { artist: 'Chris Stapleton', name: 'Traveller', sales: 1085000 }, { artist: 'Pentatonix', name: 'A Pentatonix Christmas', sales: 904000 }, { artist: 'Original Broadway Cast Recording', name: 'Hamilton: An American Musical', sales: 820000 }, { artist: 'Twenty One Pilots', name: 'Blurryface', sales: 738000 }, { artist: 'Prince', name: 'The Very Best of Prince', sales: 668000 }, { artist: 'Rihanna', name: 'Anti', sales: 603000 }, { artist: 'Justin Bieber', name: 'Purpose', sales: 554000 } ]; var totalAlbumSales=musicData.filter((curr) => curr.artist.length + curr.name.length < 25); console.log(totalAlbumSales); 

Answer 3

You weren't returning from the filtering function. Here you go.

 const musicData = [ { artist: 'Adele', name: '25', sales: 1731000 }, { artist: 'Drake', name: 'Views', sales: 1608000 }, { artist: 'Beyonce', name: 'Lemonade', sales: 1554000 }, { artist: 'Chris Stapleton', name: 'Traveller', sales: 1085000 }, { artist: 'Pentatonix', name: 'A Pentatonix Christmas', sales: 904000 }, { artist: 'Original Broadway Cast Recording', name: 'Hamilton: An American Musical', sales: 820000 }, { artist: 'Twenty One Pilots', name: 'Blurryface', sales: 738000 }, { artist: 'Prince', name: 'The Very Best of Prince', sales: 668000 }, { artist: 'Rihanna', name: 'Anti', sales: 603000 }, { artist: 'Justin Bieber', name: 'Purpose', sales: 554000 } ]; var totalAlbumSales=musicData.filter((curr) => { return curr.artist.length+curr.name.length <25 }) console.log(totalAlbumSales)