Scrimba's JavaScript Deep Dive - Part IV

Array & Sets

• More flexible than Objects
• indexOf= -1 means the value does not exist in the array. We can use includes or some (like callback functions). We also have every to review a condition in all elements of the array
• map method return an array of the same length, if we want a subset of the array, we can use the method filter. But if there is not element matching, we will get an empty array.
• Also we can use reduce can also be used, but need more arguments. This is the most powerful method for arrays
• push to add elements to array, but it will replicate to other arrays with reference (as array is a subtype of objects). We can use concat to copy and add values, or use spread operators to clone arrays and slice
• object.keys(): allow to generate an array and use the key names
• Set don't count equal elements, unless they are in [i], as they will be arrays. We can use this method to find the unique data sets
• Array methods: map(), filter(), reduce(), some()/every(), find()/findeIndex(), forEach(). Plus: slice(), concat(), includes() + spread. Use the best for each case, that makes the code easier to write and follow