The Problem

• a challenge that the user has

The Need

• the need that the user would like met

The Ask

• the specific thing that would meet the need

Input

Output

Declare a local variable

var name; // declare but do not initialize
var name = value; // declare and initialize
let name [= value]; // block-scoped variable declaration
const name = value; // block-scoped constant
// Note: const can't be reassigned or redeclared

Declare an empty array

var a = [];

Push elements onto the array

a.push( value )

Access a particular element in the array

a[i]

Sort the array in default (string) order

a.sort() // Only applies to arrays, not strings

Iterate over the elements in the array

for ( i in a ) { v = a[i]; ... }

Make a copy of an array

var b = a.slice()

Declare an empty object / hash-map

var h = {};

Add a new key/value pair

h.key = "value" or h["key"] = "value"

Access the value stored for a particluar key

h.key or h["key"]

Test if the key exists already

h.hasOwnProperty( "key" )

Iterate over the keys

for ( k in h ) { v = h[k]; ... }

Compare arrays or hash/objects

Javascript provides no built-in mechanism for deep comparison, you must roll-your-own

Get the length of a string

var s = "foo"; s.length == 3

Access the nth character in a string

var s = "foo";
s[0] == "f"; // faster, but doesn't work on IE7
s.charAt(0) == "f"; // slower, but universally supported

Find the first instance of character/substring

var s = "foo";
s.indexOf('o') == 1; // 0-based indexing
s.indexOf('x') == -1; // -1 for not found

Replace all instances of character X with character Y

s.replace(/X/g, 'Y' )

Convert a string to an array of characters

var s = "foo";
// intent: a = [ 'f', 'o', 'o' ]
var a = [...s]; // option 1 - spread operator
var a = s.split(''); // option 2 - split function

Concatenate the elements of an array into a string

var s = a.join('');

Increment/decrement a variable

x += 1 or x -= 1

Get or test the type of a variable

typeof "foo" === "string" and
typeof 42 === "number" and
typeof {foo:"bar"} === "object" and
typeof [1,2,3] === "object"