JavaScript, ES6, OOP Interview Questions

What is a JavaScript Closure

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Terms in this set (43)

A closure is a function defined inside another function and has access to variables that are declared and defined in the parent function scope.

What is hoisting?

Hoisting is JavaScripts default moving of variable and function declarations to the top. Even though a variable or function is declared below it being called, it's definition is hoisted, so an error is not thrown. Function declarations are hoisted, while function expressions are not.

What is Functional Programming?

Functional programming involves using pure functions that avoid shared state, mutating data, and side-effects. It is declarative, rather than imperative.

Rather than using functions to mutate a variable, functions take the value of the variable as a new variable and return a mutated version of the new variable. This allows the original variable to remain unchanged.

What is the difference between synchronous code and asynchronous code?

Synchronous code equates to 'blocking'. Blocking is basically slowing down code by not allowing the call stack (order of events) to continue until a slow 'block' is complete.

Asynchronous code uses callbacks to avoid blocking the call stack by threading the callback out to an api and then adding them to the callback stack once the api has finished the computation. The callback stack waits to be added to the call stack until the call stack is empty.

ES6: Define var vs. let vs. const

var = function scoped, classic nomenclature.

let = block scoped, solves var's problem of single binding of variables created in the for loop head. ie. "for(i=0;...".

const = block scoped, immutable value,

ES6: arrow function definitions

With params:
var sayIt = x => alert(x);

Without params:
var sayIt = () => alert('say stuff');

ES6: template literals

New way of concatenation:
- back ticks for string designation instead of quotes.
- ${} to surround injected JS variables.
- strings can span multiple lines.

ie.

var name = 'Awesome Person';
var greeting = `Hello, I'm $(name).`

SQL: Write a SQL Query that retrieves all rows from table People with brown eyes

"SELECT * FROM People WHERE eyes = brown"

SQL: Write a SQL Query that inserts a row to table People with blue eyes

"INSERT INTO People (eyes) VALUES ('blue')"

Node.js: import module Stuff from file things.js

const stuff = require('./things');