Useful Functions

Map function

will duplicate an array to another
This will retrieve the ages of everyone 18 or over and add them to the array full

var ages[12, 13, 16, 21]
var full = ages.map(function(curr){
return cur >=18;
})

This will get the 'true' boolean value of ages>= 18 then we have to use the indexOf to find the element position

console.log(ages[full.indexOf(true)]);

ES6 Equivalent This returns the index

var index = ages.findIndex(cur => cur >= 18);

This returns the actual age

var ageover18 = ages.find(cur => 18);

Apply

 function addFourAges(a,b,c,d){
 return a+b+c+d;
 };
 var sum1 = addFourAges(18,19,20,21);

Each age is passed as a variable to the function, but if the ages were in an array, we can use the apply method to pass them into the function

var ages = [18,21,22,23];
var sum2 = addFourAges.apply(null, ages);
// the null refers to the this 

ES6 Equivalent Spread Operator

const sum3 = addFourAges(...ages);
// the ... means the ages array is expanded into individual components.

Join two Arrays

Split

Used to split text given a delimiter into an array of substrings

var myText = 'hello-1'
var mysplit = myText.split('-')

Will Yield

['hello', 1]