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Array.from({length: 3}); 
// result: [undefined, undefined, undefined]

// Array.from's second argument is a mapping function. 
Array.from({length: 3}, (currentValue, index) => index);
// result: [0, 1, 2];
   

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const prefix = (prefix, value) => `${prefix}${value}`;
prefix('super ', 'dog'); // 'super dog';

// We can’t use our new prefix function inside of the array methods.

animals.map(prefix('super ');
// Result: TypeError: undefined super is not a function
            

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/**
 * Numbers:
 * We can reduce an array of numbers, to find the total. Using a number as initial value
 **/
const numbers = [5, 10, 25, 40];

numbers.reduce((accumulator, currentValue) => accumulator + currentValue, 0); // result: 80

// if we pass 10 as the initial value

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const myValues = [1.34, 3.5, 3.6, 4.1];

myValues.map(Math.round) // [1, 4, 4, 4];
   

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const myAnimals = ['dog', undefined, 'cat', 'bird', undefined, 0, false];

myAnimals.filter(Boolean); // Result: ['dog', 'cat', 'bird'];

/* 
    it will call Boolean('dog'), then Boolean(undefined), 
    then Boolean('cat') etc etc, the array.filter() callback must return true to keep
    an element in the array, if its false it excludes it
*/

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const superSize = value => `super ${value};

animals.map(superSize);
// result: ['super dog', 'super cat', 'super bird'];
   

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const animals = ['dog', 'cat', 'bird', 'giraffe'];

// es5
animals.map(function(currentValue, index, array) {
  return 'super ' + currentValue;
});

//es6
animals.map((currentValue, index, array) => `super ${currentValue}`);

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users.map(getValue('id')); 
// result: ['12345', '34325', '42524']
   

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const getValue = property => obj => obj && obj[property];

// Example List of users
const users = [{
    name: 'sarah',
    id: '12345',
    country: 'Australia',
},
{

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// example of a higher order function: .map() on arrays, map expects a function callback
[1,2,3].map(num => num + 1); // [2, 3, 4];

// closures in es5 syntax
function getValue(property) {
    return function(obj) {
        return obj && obj[property];
    }
}