Define

var data = [];
var assorted = [1, 'Hi', true];
assorted[0]; // 1
assorted.length; // 3

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Add & Remove

1. Assign – Assigning a value

var numbers = [1, 2, 3, 4, 5, 6];
numbers[6] = 7;  //Result: [1, 2, 3, 4, 5, 6, 7] 

2. Push – Adding to the end of the array

numbers.push(8, 9);  //Result: [1, 2, 3, 4, 5, 6, 7, 8, 9]

3. Unshift – Adding to the beginning of the array

numbers.unshift(0);      // Result: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
numbers.unshift(-2, -1); //Result: [-2, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

Remove items

numbers.pop();    //Result: [-2, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8]
numbers.shift();  //Result: [-1, 0, 1, 2, 3, 4, 5, 6, 7, 8]

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Iteration

for ( var i = 0; i < list.length; i += 1) {
  listHTML += '<li>' + list[i] + '</i>';
}

Array Iteration Practice

function printList( list ) {
  var listHTML = '<ol>';
  for ( var i = 0; i < list.length; i += 1) {
    listHTML += '<li>' + list[i] + '</i>';
  }
  listHML += '</ol>'
  return listHTML
}

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Array Methods

join(), concat(), indexOf()

var workDays = ['Monday','Tuesday','Wednesday','Thursday','Friday'];
var weekendDays = ['Saturday','Sunday'];
workDays.join(', ');          // Returns a string of list items separated by a comma
workDays.concat(weekendDays); // Adds an array to an array
workDays.indexOf('Monday');   // Returns 0. If item is recurring, it returns first one's index. If item doesn't exist, it returns -1

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2D Arrays Practice

var grades = [
  [80, 90, 100, 95], 
  [75, 95, 85, 100], 
  [60, 80, 77, 90]
];
grades[0][3]; // 95

Example

var userAnswer = "";
var correctAnswers = 0;
var questions = [
  ["Quesion one?", "Answer 1"], 
  ["Quesion two?", "Answer 2"], 
  ["Quesion three?", "Answer 3"]
];

for (var i = 0; i < questions.length; i += 1) {
  userAnswer = prompt( questions[i][0] );
  if ( userAnswer === questions[i][1] ){
    correctAnswers += 1;
    console.log("Correct!");
  } else {
    console.log("Wrong!");
  }
}
console.log