[ES6] 10. Array Comprehensions

ES6 decided that Array Comprehensions will not included in this version, ES7 will include this. Therefore, only FireFox support this, you can test it under FireFox Firebug.

Since CoffeeScrip also has array comprehension, let's go over how it looks in CoffeeScript first:

for person in people
　　console.log(person.name) if person.age > 18

console.log "#{person.name}" for person in people when person.age > 18
// In coffeeScrip,
//<expression> for <elm> in <list> when <elm> <condition>

Array Comprehensions:

var people = [
    {
        firstName: "Allen",
        secondName: "Hook",
        email: "allen@abc.com"
    },
    {
        firstName: "Anton",
        secondName: "Tee",
        email: "tee@abc.com"
    },
    {
        firstName: "Yui",
        secondName: "Gegg",
        email: "gegg@abc.com"
    }
];

For example, I have a list of people, and I want to get all the emails into a spreate array:

var emails = [for(person of people) person.email];
console.log(emails);

If:

you can add if segement as well after for..of:

var emails = [for(person of people) if(person.firstName === "Yui") person.email];
console.log(emails); // ["gegg@abc.com"]

Mutli for..of:

var nums = [1, 2, 3, 4, 5];
var letters = ["a", "b", "c", "d", "e"]

var battleship = [for(num of nums) for(letter of letters) num + letter]

console.log(battleship);

// ["1a", "1b", "1c", "1d", "1e", "2a", "2b", "2c", "2d", "2e", "3a", "3b", "3c", "3d", "3e", "4a", "4b", "4c", "4d", "4e", "5a", "5b", "5c", "5d", "5e"]

var nums = [1, 2, 3, 4, 5];
var letters = ["a", "b", "c", "d", "e"]

var battleship = [for(num of nums) [for(letter of letters) num + letter]]

console.log(battleship);

// [["1a", "1b", "1c", 2 more...], ["2a", "2b", "2c", 2 more...], ["3a", "3b", "3c", 2 more...], ["4a", "4b", "4c", 2 more...], ["5a", "5b", "5c", 2 more...]]

String can also be considered as an 'array':

let letter = [for (letter of 'abcde') if (/[aeiou]/.test(letter)) letter].join('');

console.log(letter); // ae