- Function expressions are best for object methods. Arrow functions are best for callbacks or methods like map , reduce , or forEach . Use function declarations for functions you'd call by name (because they're hoisted). Use arrow functions for callbacks (because they tend to be terser).
- Unlike regular functions, arrow functions do not have their own this . The value of this inside an arrow function remains the same throughout the lifecycle of the function and is always bound to the value of this in the closest non-arrow parent function.
- An arrow function doesn't have its own this value and the arguments object. Therefore, you should not use it as an event handler, a method of an object literal, a prototype method, or when you have a function that uses the arguments object.
var:
- hoisted (always declared at top of scope, global if none)
- function scope
let:
- block scope
- not redeclarable
const:
- block scope
- not reassignable
- not redeclarable
Template literals are literals delimited with backtick (`) characters, allowing for multi-line strings, for string interpolation with embedded expressions, and for special constructs called tagged templates.
Template literals are sometimes informally called template strings, because they are used most commonly for string interpolation (to create strings by doing substitution of placeholders). However, a tagged template literal may not result in a string; it can be used with a custom tag function to perform whatever operations you want on the different parts of the template literal.