Map the Debris
Problem Explanation
The first thing to do is to get familiar with what the program is for by knowing what Orbital period exactly is. You’ve to return a new array that transforms the element’s average altitude into their orbital periods. The parts generally found hard are finding the formula, implementing it and for some people, modifying objects by the key. However, something that is not very clear is the fact that your program has to be able to check for any number of objects in the array; This is what is tested on the second part.
Relevant Links
Hints
Hint 1
The formula needed is:
Hint 2
Use Math.round()
to round up to the next whole number as requested. Using Math.ceil()
will let you pass the first test but fail the second one.
Hint 3
Find out how to remove and add key to a JavaScript object.
Solutions
Solution 1 (Click to Show/Hide)
function orbitalPeriod(arr) {
var GM = 398600.4418;
var earthRadius = 6367.4447;
var a = 2 * Math.PI;
var newArr = [];
var getOrbPeriod = function(obj) {
var c = Math.pow(earthRadius + obj.avgAlt, 3);
var b = Math.sqrt(c / GM);
var orbPeriod = Math.round(a * b);
// create new object
return {name: obj.name, orbitalPeriod: orbPeriod};
};
for (var elem in arr) {
newArr.push(getOrbPeriod(arr[elem]));
}
return newArr;
}
// test here
orbitalPeriod([{ name: "sputnik", avgAlt: 35873.5553 }]);
Code Explanation
- GM and earthRadius are both given to us.
- To make the code easier to edit and read, each part of the equation is written separately.
- Create newArr to store the
orbPeriod
's. - a is 2 times pi. The part that is a constant is on the global scope while the rest is part of a function.
- Create a function,
gerOrbPeriod()
that will do the required work for any amount of objects. - c is (earthRadius + avgAlt) to the cube.
- b is the square root of c divided by GM.
- Create orbPeriod to store the product of a and b, with the
Math.round()
function applied to round up to the next whole number. - Then we delete the key avgAlt, and add the new key and its value.
Relevant Links
Solution 2 (Click to Show/Hide)
function orbitalPeriod(arr) {
var GM = 398600.4418;
var earthRadius = 6367.4447;
var newArr = [];
//Looping through each key in arr object
for (var elem in arr) {
//Rounding off the orbital period value
var orbitalPer = Math.round(
2 * Math.PI * Math.sqrt(Math.pow(arr[elem].avgAlt + earthRadius, 3) / GM)
);
//Adding new object with orbitalPeriod property
newArr.push({name: arr[elem].name, orbitalPeriod: orbitalPer});
}
return newArr;
}
// test here
orbitalPeriod([{ name: "sputnik", avgAlt: 35873.5553 }]);
Code Explanation
- GM and earthRadius are both given to us.
- A
for..in
loop is used to iterate through each value in given array arr. - orbitalPer holds the value of orbital period for each iteration calculated using the formula.
- The key avgAlt is deleted, and orbitalPer found is assigned in arr.
Solution 3 (Click to Show/Hide)
function orbitalPeriod(arr) {
var GM = 398600.4418;
var earthRadius = 6367.4447;
// Create new array to prevent modification of the original
var newArr = JSON.parse(JSON.stringify(arr));
// Loop through each item in the array arr
newArr.forEach(function(item) {
// Calculate the Orbital period value
var tmp = Math.round(
2 * Math.PI * Math.sqrt(Math.pow(earthRadius + item.avgAlt, 3) / GM)
);
//Delete the avgAlt property
delete item.avgAlt;
//Add orbitalPeriod property
item.orbitalPeriod = tmp;
});
return newArr;
}
// test here
orbitalPeriod([{ name: "sputnik", avgAlt: 35873.5553 }]);
Code Explanation
- GM and earthRadius are both given to us.
- The
forEach()
method is used to execute the function once per element (item) in arr. - tmp holds the value of orbital period for each element calculated using the formula.
- The key avgAlt is deleted, and orbital period (tmp) found is assigned to the key orbitalPeriod.
Relevant Links
Solution 4 (Click to Show/Hide)
function orbitalPeriod(arr) {
const GM = 398600.4418;
const earthRadius = 6367.4447;
return arr.map(({ name, avgAlt }) => {
const earth = earthRadius + avgAlt;
const orbitalPeriod = Math.round(2 * Math.PI * Math.sqrt(Math.pow(earth, 3)/GM));
return { name, orbitalPeriod };
});
}
orbitalPeriod([{name : "sputnik", avgAlt : 35873.5553}]);