08-functional-programming.md

What are callbacks?

Functions that are passed into another function to decide the invocation of that function.

What are first class functions?

Function that

• can be assigned to a variabled
• passed into another function
• returned from another function

What are higher order functions?

Functions that

• take a function as an argument
• return a function

What is a lambda?

A function that is

• passed in another function
• returned from another function

How do I use map?

users.map(user => user.name)

What are the arguments of the map callback?

• element
• index
• array

How do I get a copy of a subset of an array?

array.slice(inclusiveStartIndex, exclusiveEndIndex)

How do I get a copy of an array using slice?

array.slice()

What does reduce do?

Iterates over each item in array and returns single value

// reduce(callback, initialValueOfAccumulator)
users.reduce((sum, user) => sum + user.age, 0)

What are the arguments of the reduce callback?

• accumulator

  • assigned return value of callback

• element

• index

• array

What is the default sorting method of Array.prototype.sort?

Unicode point value

Does Array.prototype.sort mutate the array?

Yes :(

How do I check if all items in an array meet a criteria?

Array.prototype.every

How do I check if some items in an array meet a criteria?

Array.prototype.some

What do you call the number of arguments of a function?

Its arity

What is currying?

Convert a function of N arity into N functions of arity 1.

//Curried function
function curried(x) {
  return function(y) {
    return x + y;
  }
}

What is partial application?

Applying a few arguments to a function at a time and returning another function that is applied to more arguments.

//Impartial function function impartial(x, y, z) { return x + y + z; } var partialFn = impartial.bind(this, 1, 2); partialFn(10); // Returns 13