javascript.md

title	Javascripting
kind	cheatsheet
keywords	code cheatsheet
created_at	2015-aug-12 09:59:00

Javascript

console.log() is your friend.

'use strict'; enables strict mode, use it!

variables

Variable declarations are hoisted to the top of the enclosing scope always.

// assigning something to a variable just like that makes it global!!!
blah = "hello"

// using 'var' makes the declaration local to the enclosing function
var blah = "hello"

// using 'let' makes the variable local to the block
let blah = "hello";

// 'const' makes the variable a constant (assignment only on declaration), local within block
const blah = "hello"

strings

var example = 'some string';
console.log(example.length);

var numToString = 0.5.toString();

var linesAsArray = myString.split('\n');

Numbers

var rounded = Math.round(0.5);

var num = Number('3.14');

Operators

==, and != only test for value equalty 5 == "5" // true
===, and !== operators test for value AND type 5 === "5" // false

Loops

for(var i=0; i<10; i++) {
  console.log(i);
}

Arrays

var pets = ['cat', 'dog', 'elephant'];
pets.push('dolphin');

for(var i=0; i<pets.length; i++) {
  console.log(pets[i]);
}

var filtered = pets.filter(function(pet) {
  return (pet !== 'elephant');
});

Objects

var pizza = {
  toppings: ['cheese', 'sauce', 'pepperoni'],
  crust: 'deep dish',
  serves: 2
}

// two ways for accessors:
console.log(pizza.crust);
console.log(pizza['serves']);

Functions

Functions are first class citizens in javascript.

Functions defined inside other functions have access to their parent function's scope.

function multiply(x, mult) {
  return x*mult;
}

multiply(2, 4);

IIFE (Immediately Invoked Function Expression) is a common pattern for creating local scopes:

(function() {
  // variables defined here can't be accessed outside
})(); // the function is immediately invoked