freecodecamp: basic data structures

I note passed challenge code for help.

Use an Array to Store a Collection of Data

"let yourArray=[1,true,"3",4,5]; // change this line"

 Access an Array's Contents Using Bracket Notation

"myArray[1]="bb";"

Add Items to an Array with push() and unshift()

" arr.unshift("I",2,"three");

arr.push(7,"VIII",9);"

 Remove Items from an Array with pop() and shift()

"let popped=arr.pop(); // change this line

let shifted=arr.shift(); // change this line"

Remove Items Using splice()

" // change code below this line

arr.splice(2,2);

// change code above this line"

Add Items Using splice()

" // change code below this line

arr.splice(0,2,'DarkSalmon','BlanchedAlmond');

// change code above this line

"

Copy Array Items Using slice()

" // change code below this line

arr= arr.slice(2,4);

return arr;"

Copy an Array with the Spread Operator

" // change code below this line

newArr.push([...arr]);

// change code above this line"

Combine Arrays with the Spread Operator

"let sentence=['learning',...fragment,'is','fun']; // change this line"

Check For The Presence of an Element With indexOf()

" // change code below this line

if(arr.indexOf(elem)=== -1)

return false;

else

return true;

// change code above this line"

Iterate Through All an Array's Items Using For Loops

" // change code below this line for(let i=0;i<arr.length;i++){ if(arr[i].indexOf(elem)== -1){ newArr.push(arr[i]); } } // change code above this line"

Create complex multi-dimensional arrays

" // change code below this line

['unshift', false, 1, 2, 3, 'complex', 'nested'],

['loop', 'shift', 6, 7, 1000, 'method'],

['concat', false, true, 'spread', 'array'],

['mutate', 1327.98, 'splice', 'slice', 'push'],

[[[['deepest', 1.3849, 7], 'deeper'], 'deep'], 'depth']

// change code above this line"

Add Key-Value Pairs to JavaScript Objects

"// change code below this line

foods.bananas=13;

foods.grapes=35;

foods.strawberries=27;

// change code above this line"

 Modify an Object Nested Within an Object

"userActivity.data.online=45;"

Access Property Names with Bracket Notation

"return foods[scannedItem];"

Use the delete Keyword to Remove Object Properties

" delete foods.oranges;

delete foods.plums;

delete foods.strawberries;"

Check if an Object has a Property

" if('Alan','Jeff','Sarah','Ryan' in obj)

return true;

else

return false;"

Iterate Through the Keys of an Object with a for...in Statement

" let count=0;

for(let u in obj){

if(obj[u].online)

count+=1;

;

}

return count;"

Generate an Array of All Object Keys with Object.keys()

"return Object.keys(obj);"

Modify an Array Stored in an Object

"userObj.data.friends.push(friend); return userObj.data.friends;"