Arrayzing - The JavaScript array cheatsheet

arrayzing.md

Arrayzing - The JavaScript array cheatsheet

This is a work-in-progress cheatsheet for JS arrays. Please feel free to leave a comment if this has helped you or you would like to suggest anything.

• Create an array
• Empty an array
• Clone an array
• Get last item
• Remove first item
• Remove last item
• Add new item(s) to beginning
• Add new item(s) to end
• Overwrite item at a specific index
• Add new item(s) at a specific index
• Remove single item at a specific index
• Remove several items
• Reverse an array
• Delimit an array
• Sort in numerical order
• Sort in alphabetical order
• Join two arrays together
• Copy specific item(s)
• Augment items within an array
• Return true if every item meets a condition
• Return true if at least one item matches a condition
• Execute a function once per array item
• Filter an array
• Detect an array
• ES5 and above
• ES4 and below
• Simple FIFO queue
• Find index of an item
• ES5 and above
• ES4 and below
• Randomise an array
• Chaining Methods

Create an array

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

Empty an array

Keeping references intact.

var meals = ['breakfast', 'lunch', 'dinner'];
meals.splice(0, meals.length);

or

var meals = ['breakfast', 'lunch', 'dinner'];
meals.length = 0

Clone an array

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

var copy = meals.slice();
// ['breakfast', 'lunch', 'dinner']

Get last item

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

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

Or

var meals = ['breakfast', 'lunch', 'dinner'];
meals.slice(-1)[0];
// 'dinner'

Remove first item

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

meals.shift();
// 'breakfast'

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

Remove last item

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

meals.pop();
// 'dinner'

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

Add new item(s) to beginning

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

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

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

Add new item(s) 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);
// ['lunch', 'dinner']

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 order

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

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

Sort in numerical order

var numbers = [1438,2605,794,3947,6241,11745,2585];

numbers.sort(function(a, b) {
    return a - b;
});
// [794,1438,2585,2605,3947,6241,11745]

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'];

meals.filter(function(item) {
  return item !== 'breakfast';
});
// ['lunch', 'dinner', 'supper'];

Detect an array

ES5 and above

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

Array.isArray(meals)
// true

ES4 and below

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

function isArray(arr) {
  return !!(Object.prototype.toString.call(arr) === '[object Array]');
}

isArray(meals);
// true

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 ...

Find index of an item

ES5 and above

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

ES4 and below

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

function inArray(arr, item){
  var found = -1, 
      i = arr.length; 

  while(--i >= 0) {
    if(arr[i] === item){
      found = i;
      break;
    }
  }
  return found;
}

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

inArray(meals, 'dinner');
// -1

Randomise an array

function randomiseArray(arr) {
    var buffer = [], start;

    for(var i = arr.length; i >= arr.length && i > 0;i--) {
        start = Math.floor(Math.random() * arr.length);
        buffer.push(arr.splice(start, 1)[0])
    };

    return buffer;
}

randomiseArray([0,1,2,3,4]);
// [2,1,0,3,4]

randomiseArray([0,1,2,3,4]);
// [3,2,1,4,0]

randomiseArray([0,1,2,3,4]);
// [1,2,4,0,3]

Chaining methods

var meals = [
  {type: 'breakfast', name: 'Full English', calories: 1500},
  {type: 'breakfast', name: 'Colacao', calories: 260},
  {type: 'breakfast', name: 'Croissant and jam', calories: 520},
  {type: 'breakfast', name: 'Granola with Greek yoghurt and blueberries', calories: 680},
  {type: 'brinner', name: 'Shepherds Pie with strawberry yoghurt', calories: 915},
  {type: 'brinner', name: 'Milky Porridge with beef and green beans', calories: 875},
  {type: 'dinner', name: 'Phad Thai', calories: 750},
  {type: 'dinner', name: 'Chicken Katsu curry and rice', calories: 830},
];

function getMealsByMaxCalories(meals, maxCalories, dailyAllowance) {
  return meals
    .filter(function(meal) {
        return meal.calories <= maxCalories;
    })
    .map(function(meal) {
        return {
            name: meal.name,
            calories: meal.calories,
            percentageOfDailyAllowance: meal.calories / dailyAllowance * 100
        }
    });
}
    
getMealsByMaxCalories(meals, 850, 2000);

/*
[
  {
    "name": "Colacao",
    "calories": 260,
    "percentageOfDailyAllowance": 13
  },
  {
    "name": "Croissant and jam",
    "calories": 520,
    "percentageOfDailyAllowance": 26
  },
  {
    "name": "Granola with Greek yoghurt and blueberries",
    "calories": 680,
    "percentageOfDailyAllowance": 34
  },
  {
    "name": "Phad Thai",
    "calories": 750,
    "percentageOfDailyAllowance": 37.5
  }
]
*/

LICENSE

The MIT License (MIT)

Copyright (c) 2015 Justin Perry

Permission is hereby granted, free of charge, to any person obtaining a copy of
this software and associated documentation files (the "Software"), to deal in
the Software without restriction, including without limitation the rights to
use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
the Software, and to permit persons to whom the Software is furnished to do so,
subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.