Array Cheatsheet

arrayzing.md

Array Cheatsheet

Creating an array

var meals = ['breakfast', 'lunch', 'dinner'] ;

Or

var meals = new Array('breakfast', 'lunch', 'dinner');

Getting last item

var meals = ['breakfast', 'lunch', 'dinner'];

meals[meals.length - 1];
// 'dinner'

meals.slice(-1);
// 'dinner'

Remove first item

var meals = ['breakfast', 'lunch', 'dinner'];

['breakfast', 'lunch', 'dinner'].shift();
// 'breakfast'

meals;
// ['lunch', 'dinner']

Remove last item

var meals = ['breakfast', 'lunch', 'dinner'];

meals.pop();
// 'dinner'

meals;
// ['breakfast', 'lunch'];

Add new item to beginning

var meals = ['lunch', 'dinner'];

meals.unshift('breakfast');
// 3 - the array length

meals;
// ['breakfast', 'lunch', 'dinner']

Add new item to end

var meals = ['breakfast', 'lunch', 'dinner'];

meals.push('supper');
// 2

meals;
// ['breakfast', 'lunch', 'dinner', 'supper'];

Overwrite item at a specific index

var meals = ['breakfast', 'lunch', 'dinner'];

meals[1] = 'brunch';
// ['breakfast', 'brunch', 'dinner'];

Or

var meals = ['breakfast', 'lunch', 'dinner'];

meals.splice(1, 1, 'brunch');

Add new item(s) at a specific index

var meals = ['breakfast', 'lunch', 'dinner'];

meals.splice(1, 0, 'brunch', 'more brunch');
// ['breakfast', 'brunch', 'more brunch', 'lunch', 'dinner']

Remove single item at a specific index

var meals = ['breakfast', 'lunch', 'dinner'];

meals.splice(1, 1);
// ['lunch']

meals;
// ['breakfast', 'dinner']

Remove several items

var meals = ['breakfast', 'lunch', 'dinner'];

meals.splice(1, 2);
// ['breakfast']

meals;
// ['breakfast']

Reverse an array

var meals = ['breakfast', 'lunch', 'dinner'];

meals.reverse();
// ['dinner', 'lunch', 'breakfast'];

Delimit an array

var meals = ['breakfast', 'lunch', 'dinner'];

meals.join(' AND ');
// 'breakfast AND lunch AND dinner'

Sort in alphabetical/numerical order

var meals = ['breakfast', 'lunch', 'dinner'];

meals.sort();
// ['breakfast', 'dinner', 'lunch']

Sort in reverse alphabetical/numerical order

[0, 1, 2, 3, 4, 5, 6].sort(function(a, b) {
  return b > a;
});
// [6, 5, 4, 3, 2, 1, 0]

Or

[0, 1, 2, 3, 4, 5, 6].sort().reverse();
// [6, 5, 4, 3, 2, 1, 0]

Join two arrays together

var dayTimeMeals = ['breakfast', 'lunch'];
var nightTimeMeals = ['merienda', 'dinner'];

var allTheMeals = dayTimeMeals.concat(nightTimeMeals);
// ['breakfast', 'lunch', 'merienda', 'dinner']

Copy specific item(s)

var meals = ['breakfast', 'lunch', 'dinner', 'supper'];

nightTimeMeals = meals.slice(2,4);
// ['dinner', 'supper']

Augment items within an array

var meals = ['breakfast', 'lunch', 'dinner'];
var type = ['king', 'prince', 'pauper'];

meals.map(function(item, i) {
  return item + ' like a ' + type[i];
});
// ["breakfast like a king", "lunch like a prince", "dinner like a pauper"]

Return true if every item meets a condition

var meals = ['breakfast', 'lunch', 'dinner', 'supper'];

meals.every(function(item){ return item.length > 0 });
// true

meals.every(function(item){ return item.length > 6 });
// false

Return true if at least one item matches a condition

var meals = ['breakfast', 'lunch', 'dinner', 'supper'];

meals.some(function(item){ return item === 'lunch';});
// true

meals.some(function(item){ return item === 'burgers!!';});
//false

Execute a function once per array item

var meals = ['breakfast', 'lunch', 'dinner', 'supper'];
meals.forEach(function(currentValue, index, arr){
  console.log(index, currentValue, arr);
});

Filter an array

var meals = ['breakfast', 'lunch', 'dinner', 'supper'];

function skipBreakfast(item) {
  return item !== 'breakfast';
}

meals.filter(skipBreakfast);
// ['lunch', 'dinner', 'supper'];

Simple FIFO queue

var meals = ['breakfast', 'elevenses', 'brunch'];

meals.shift(); 
meals.push('lunch');

// ['elevenses', 'brunch', 'lunch']

meals.shift()
meals.push('afternoon tea');

// ['brunch', 'lunch', 'afternoon tea']
// ... and so on ...

Check if an item is in an array

ES4 and below

var meals = ['breakfast', 'elevenses', 'brunch'];

function inArray(arr, query){
  var found = false,
      len = arr.length, 
      i = 0; 

  for(; i < len; i++){
    if(arr[i] === query){
      found = i;
    }
  }
  return found;
}

inArray(meals, 'brunch');
// 2 - the index of the item in the array

inArray(meals, 'dinner');
// false

ES5 and above

var meals = ['breakfast', 'elevenses', 'brunch'];
meals.indexOf('brunch');
// 2