Javascript Array

myArray.length;
myArray[0]; // the first item in the array
myArray[1]; // the second item in the array
myArray[myArray.length-1]; // the last item in the array

let myNewString = myArray.join(',');
myNewString;

let dogNames = ['Rocket','Flash','Bella','Slugger'];
dogNames.toString(); // Rocket,Flash,Bella,Slugger

Add remove array items
push()
pop()

let myArray = ['Manchester', 'London', 'Liverpool', 'Birmingham', 'Leeds', 'Carlisle'];

myArray.push('Cardiff');
myArray;
myArray.push('Bradford', 'Brighton');
myArray;

从头开始加入和删除
unshift()
shift()



const list = document.querySelector('.output ul');
const searchInput = document.querySelector('.output input');
const searchBtn = document.querySelector('.output button');

list.innerHTML = '';

let myHistory = [];

searchBtn.onclick = function() {
  // we will only allow a term to be entered if the search input isn't empty
  if (searchInput.value !== '') {
    // number 1
    myHistory.unshift(searchInput.value);
    
    // empty the list so that we don't display duplicate entries
    // the display is regenerated every time a search term is entered.
    list.innerHTML = '';

    // loop through the array, and display all the search terms in the list
    for (let i = 0; i < myHistory.length; i++) {
      itemText = myHistory[i];
      const listItem = document.createElement('li');
      listItem.textContent = itemText;
      list.appendChild(listItem);
    }

    // If the array length is 5 or more, remove the oldest search term
    if (myHistory.length >= 5) {
      // number 2
      myHistory.pop();

    }

    // empty the search input and focus it, ready for the next term to be entered
    searchInput.value = '';
    searchInput.focus();
  }
}


splice  剪接
reverse  颠倒
sort  排序

let sortFn = function(a, b) {
  if (a[a.length - 1] < b[b.length - 1]) return -1;
  if (a[a.length - 1] > b[b.length - 1]) return 1;
  if (a[a.length - 1] == b[b.length - 1]) return 0;
}
myArray.sort(sortFn)
// sorts the array so that myArray = ["Wind","Fire","Rain"]


forEach

map()
filter()
every()
some(callback[, thisObject])  some(callback[, thisObject]) returns true if callback returns true for at least one item in the array.

reduce(callback[, initialVaule]

Using arrays to store other properties

Arrays can also be used like objects, to store related information.

const arr = [1, 2, 3];
arr.property = "value";
console.log(arr.property);  // Logs "value"
Some JavaScript objects, such as the NodeList returned by document.getElementsByTagName() or the arguments object made available within the body of a function, look and behave like arrays on the surface but do not share all of their methods. The arguments object provides a length attribute but does not implement the forEach() method, for example.

Array methods cannot be called directly on array-like objects.

function printArguments() {
  arguments.forEach(function(item) {  // TypeError: arguments.forEach is not a function
    console.log(item);
  });
}
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But you can call them indirectly using Function.prototype.call().

function printArguments() {
  Array.prototype.forEach.call(arguments, function(item) {
    console.log(item);
  });
}
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Array prototype methods can be used on strings as well, since they provide sequential access to their characters in a similar way to arrays:

Array.prototype.forEach.call('a string', function(chr) {
  console.log(chr)
})
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