1. JavaScript¶

JavaScript can function as both a procedural and an object oriented language.

Web browser is the runtime environment for client-side JavaScript.

Node.js is a server side environment that is operates in a similar capacity to the JVM in java

1.1. JavaScript vs ECMAScript¶

console.log("Hello World");

JavaScript is dynamically-typed and does not require type constraints

var myNum = 42;
myNum = "forty-two";

There are 3 keywords for declaration:

var - was default before ES6. But due to issues, that's why there are other ways of declaring.
- Scope: Declared global outside function. And local when declared inside the function.
- var variables can be re-declared and updated
- Hoisting of var: if var is referred to before declaration. Then interpreter assumes it was assigned to undefined
- The problem is that var can be redefined in the middle of the code, which can cause unexpected answers.
let - now used as the preferred variable declaration.
- Block scoped: (A block lives in curly braces)
- Can be updated but not re-declared
- Those two can be combined, by redeclaring variables in blocks.
- Hoisting of let: Just like var it can be hoisted on the top, but unlike var you get Reference Error
const - maintain constant values
- Block Scoped: can only be accessed within the block they were declared
- Cannot be updated or re-declared: Therefore it's constant
  - For a constant object, the object cannot be updated or redefined but the properties can be changed.
- Hoisting of const: Hoisted but no initialised just like let

There are no access modifiers like in Java, everything is accessible.

Number - equivalent to double in Java
String - no such thing as a char
Boolean
Symbol - ES6 addition
Undefined - implicitly assigned when variable is declared but not instantiated
Null - Is an explicitly assigned.