Chapter 1 A quick Intro to Base objects

1.1 Launch a REPL

  • For interactive usage
library(bubble)
node_repl()

1.2 Assignment

  • Done with =
var x = 12;

1.3 Scalar objects

1.3.1 Numbers

var y = 17;
x + y;
# 29

1.3.2 Character

var z = "plop";
# undefined
  • All objects have methods that can be accessed with obj.
z.toUpperCase();
# 'PLOP'
z.length;
# 4
  • To know all the available methods
var prot = Object.getPrototypeOf(z);
Object.getOwnPropertyNames(prot);
# undefined
# [ 'length',
#   'constructor',
#   'anchor',
#   'big',
#   'blink',
#   'bold',
#   'charAt',
#   'charCodeAt',
#   'codePointAt',
#   'concat',
#   'endsWith',
#   'fontcolor',
#   'fontsize',
#   'fixed',
#   'includes',
#   'indexOf',
#   'italics',
#   'lastIndexOf',
#   'link',
#   'localeCompare',
#   'match',
#   'normalize',
#   'padEnd',
#   'padStart',
#   'repeat',
#   'replace',
#   'search',
#   'slice',
#   'small',
#   'split',
#   'strike',
#   'sub',
#   'substr',
#   'substring',
#   'sup',
#   'startsWith',
#   'toString',
#   'trim',
#   'trimLeft',
#   'trimRight',
#   'toLocaleLowerCase',
#   'toLocaleUpperCase',
#   'toLowerCase',
#   'toUpperCase',
#   'valueOf',
#   'trimStart',
#   'trimEnd' ]

1.3.3 Boolean

var a = true;
# undefined

  • if are written as in R

  • console.log() prints to the console (useful for debugging)

if (a) {
  console.log("yeay");
}
# yeay
# undefined

1.3.4 Null & undefined

  • null is an empty, non existing value that has to be defined
null
# null
  • undefined is a declared variable that has no value

You’ll see undefined when doing assignment, it’s the return value of =

var noval;
# undefined
noval;
# undefined

1.4 Array

  • They are R vectors

  • Can’t be named

  • Access by position

Note: INDEX STARTS AT 0

1.4.1 Create

  • Can be created empty
var emptyarray = [];

This type of creation is called “Literals”

  • Can be created with values
var x = ["pouet", "plop"];
  • Can be created with the new function
var g = new Array;
# undefined
g
# []
var x = ["pouet", "plop"]; 
x[0] = "plop"
x
# [ 'plop', 'plop' ]

1.4.2 Select

  • By position, (index start at 0)
x[0]
# 'plop'
  • Filter
var poum = "plop";

x.filter(function(item){
  return item === poum
});
# undefined
# undefined
# [ 'plop', 'plop' ]

Anonymous functions can be used here (see below for more info)

x.filter(item => item === poum);
# [ 'plop', 'plop' ]

1.4.3 Manipulate

  • Iterate

with forEach

x.forEach(function(item, index) {
  console.log(index + " : " + item);
});
# 0 : plop
# 1 : plop
# undefined

with map

x.map(z => z.toUpperCase());
# [ 'PLOP', 'PLOP' ]

Example, extracted from https://colinfay.me/aoc-2019-01/

var res = [105311, 117290, 97762, 124678, 132753, 114635];
var res = res.map(x => Math.floor(x / 3) - 2);
res
# undefined
# undefined
# [ 35101, 39094, 32585, 41557, 44249, 38209 ]
  • Reduce
var add = (x, y) => x + y;
res.reduce(add)
# undefined
# 230795
  • Finding the first element
var z = [1,2,3,4,5];
z.find(z => z > 3);
# undefined
# 4
  • Test if every / some
x.every(z => z === "plop");
# true
x.some(z => z == "plop");
# true

  • Add / Suppress

    1. At the end
// Adds
x.push("bim");
x
# [ 'plop', 'plop', 'bim' ]
// Removes
x.pop();
x
# [ 'plop', 'plop' ]
  1. At start
// Adds
x.unshift("bim")
x
# [ 'bim', 'plop', 'plop' ]
// Removes
x.shift()
x
# [ 'plop', 'plop' ]
  1. By index
x.push("bim")
x.push("blam")
x
# [ 'plop', 'plop', 'bim', 'blam' ]

Takes 1 argument, starting at index 0

x.splice(0, 1)
x
# [ 'plop', 'bim', 'blam' ]

1.4.4 Transform

x.reverse();
# [ 'blam', 'bim', 'plop' ]
x.sort()
# [ 'bim', 'blam', 'plop' ]
var y = ["plaf", "plouf"]
x.concat(y)
# undefined
# [ 'bim', 'blam', 'plop', 'plaf', 'plouf' ]
x.join()  
# 'bim,blam,plop'
var z = [1, 2, 3]
z.toString()
# undefined
# '1,2,3'

1.5 Objects

  • More or less like an R list

  • Constructed with {}

var obj = {
  a: 12, 
  b: 17, 
  c: ["plaf", "plouf"],
  d: (x) => x.toUpperCase()
}
obj
# undefined
# { a: 12, b: 17, c: [ 'plaf', 'plouf' ], d: [Function: d] }
  • Access with .name
obj.a;
# 12
  • Internal methods can be used on internal objects
obj.c.map(obj.d);
# [ 'PLAF', 'PLOUF' ]

1.6 Function

  • Standard
function add(x, y){
  return x + y
}
# undefined
add(11, 13)
# 24
  • With the new constructor
var add2 = new Function('a', 'b', 'return a + b');
# undefined
add2(11, 13)
# 24
  • As an anonymous (or arrow) function
var add3 = (a, b) => a + b
# undefined
add3(11, 13)
# 24

1.7 typeof

typeof a;
typeof z;
# 'boolean'
# 'object'
ThinkR Website