索引集合类 (Indexed collections)

var arr = new Array(element0, element1, ..., elementN);
var arr = Array(element0, element1, ..., elementN);
var arr = [element0, element1, ..., elementN];

// 译者注: var arr=[4] 和 var arr=new Array(4)是不等效的，
// 后者4指数组长度，所以使用字面值(literal)的方式应该不仅仅是便捷，同时也不易踩坑

var arr = new Array(arrayLength);
var arr = Array(arrayLength);

// 这样有同样的效果
var arr = [];
arr.length = arrayLength;

var obj = {};
// ...
obj.prop = [element0, element1, ..., elementN];

// OR
var obj = {prop: [element0, element1, ...., elementN]}

var arr = [42];      // 创建一个只有唯一元素的数组:
                     // the number 42.
var arr = Array(42); // 创建一个没有元素的数组,
                     // 但是数组的长度被设置成42.

// 上面的代码与下面的代码等价
var arr = [];
arr.length = 42;

var arr = Array(9.3);  // RangeError: Invalid array length

var emp = [];
emp[0] = "Casey Jones";
emp[1] = "Phil Lesh";
emp[2] = "August West";

var arr = [];
arr[3.4] = "Oranges";
console.log(arr.length);                // 0
console.log(arr.hasOwnProperty(3.4));   // true

var myArray = new Array("Hello", myVar, 3.14159);
var myArray = ["Mango", "Apple", "Orange"]

var myArray = ["Wind", "Rain", "Fire"];

var arr = ["one", "two", "three"];
arr[2];  // three
arr["length"];  // 3

var cats = [];
cats[30] = ['Dusty'];
console.log(cats.length); // 31

var cats = ['Dusty', 'Misty', 'Twiggy'];
console.log(cats.length); // 3

cats.length = 2;
console.log(cats); // logs "Dusty,Misty" - Twiggy has been removed

cats.length = 0;
console.log(cats); // logs nothing; the cats array is empty

cats.length = 3;
console.log(cats); // [undefined, undefined, undefined]

var colors = ['red', 'green', 'blue'];
for (var i = 0; i < colors.length; i++) {
  console.log(colors[i]);
}

var divs = document.getElementsByTagName('div');
for (var i = 0, div; div = divs[i]; i++) {
  /* Process div in some way */
}

var colors = ['red', 'green', 'blue'];
colors.forEach(function(color) {
  console.log(color);
});

var array = ['first', 'second', , 'fourth'];

// returns ['first', 'second', 'fourth'];
array.forEach(function(element) {
  console.log(element);
})

if(array[2] === undefined) { console.log('array[2] is undefined'); } // true

var array = ['first', 'second', undefined, 'fourth'];

// returns ['first', 'second', undefined, 'fourth'];
array.forEach(function(element) {
  console.log(element);
})

var myArray = new Array("1", "2", "3");
myArray = myArray.concat("a", "b", "c");
// myArray is now ["1", "2", "3", "a", "b", "c"]

var myArray = new Array("Wind", "Rain", "Fire");
var list = myArray.join(" - "); // list is "Wind - Rain - Fire"

var myArray = new Array("1", "2");
myArray.push("3"); // myArray is now ["1", "2", "3"]

var myArray = new Array("1", "2", "3");
var last = myArray.pop();
// myArray is now ["1", "2"], last = "3"

var myArray = new Array ("1", "2", "3");
var first = myArray.shift();
// myArray is now ["2", "3"], first is "1"

var myArray = new Array ("1", "2", "3");
myArray.unshift("4", "5");
// myArray becomes ["4", "5", "1", "2", "3"]

var myArray = new Array ("a", "b", "c", "d", "e");
myArray = myArray.slice(1, 4); // 包含索引1，不包括索引4
                               // returning [ "b", "c", "d"]

var myArray = new Array ("1", "2", "3", "4", "5");
myArray.splice(1, 3, "a", "b", "c", "d");
// myArray is now ["1", "a", "b", "c", "d", "5"]
// This code started at index one (or where the "2" was),
// removed 3 elements there, and then inserted all consecutive
// elements in its place.

var myArray = new Array ("1", "2", "3");
myArray.reverse();
// transposes the array so that myArray = [ "3", "2", "1" ]

var myArray = new Array("Wind", "Rain", "Fire");
myArray.sort();
// sorts the array so that myArray = [ "Fire", "Rain", "Wind" ]

var 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"]

var a = ['a', 'b', 'a', 'b', 'a'];
console.log(a.indexOf('b')); // logs 1
// Now try again, starting from after the last match
console.log(a.indexOf('b', 2)); // logs 3
console.log(a.indexOf('z')); // logs -1, because 'z' was not found

var a = ['a', 'b', 'c', 'd', 'a', 'b'];
console.log(a.lastIndexOf('b')); // logs 5
// Now try again, starting from before the last match
console.log(a.lastIndexOf('b', 4)); // logs 1
console.log(a.lastIndexOf('z')); // logs -1

var a = ['a', 'b', 'c'];
a.forEach(function(element) { console.log(element);} );
// logs each item in turn

var a1 = ['a', 'b', 'c'];
var a2 = a1.map(function(item) { return item.toUpperCase(); });
console.log(a2); // logs A,B,C

var a1 = ['a', 10, 'b', 20, 'c', 30];
var a2 = a1.filter(function(item) { return typeof item == 'number'; });
console.log(a2); // logs 10,20,30

function isNumber(value){
  return typeof value == 'number';
}
var a1 = [1, 2, 3];
console.log(a1.every(isNumber)); // logs true
var a2 = [1, '2', 3];
console.log(a2.every(isNumber)); // logs false

function isNumber(value){
  return typeof value == 'number';
}
var a1 = [1, 2, 3];
console.log(a1.some(isNumber)); // logs true
var a2 = [1, '2', 3];
console.log(a2.some(isNumber)); // logs true
var a3 = ['1', '2', '3'];
console.log(a3.some(isNumber)); // logs false

var a = [10, 20, 30];
var total = a.reduce(function(first, second) { return first + second; }, 0);
console.log(total) // Prints 60

var a = new Array(4);
for (i = 0; i < 4; i++) {
  a[i] = new Array(4);
  for (j = 0; j < 4; j++) {
    a[i][j] = "[" + i + "," + j + "]";
  }
}

function printArguments() {
  Array.prototype.forEach.call(arguments, function(item) {
    console.log(item);
  });
}

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

var numbers = [1, 2, 3, 4];
var doubled = [for (i of numbers) i * 2];
console.log(doubled); // logs 2,4,6,8

var doubled = numbers.map(function(i){return i * 2;});

var numbers = [1, 2, 3, 21, 22, 30];
var evens = [i for (i of numbers) if (i % 2 === 0)];
console.log(evens); // logs 2,22,30

var evens = numbers.filter(function(i){return i % 2 === 0;});

var numbers = [1, 2, 3, 21, 22, 30];
var doubledEvens = [i * 2 for (i of numbers) if (i % 2 === 0)];
console.log(doubledEvens); // logs 4,44,60

var str = 'abcdef';
var consonantsOnlyStr = [c for (c of str) if (!(/[aeiouAEIOU]/).test(c))  ].join(''); // 'bcdf'
var interpolatedZeros = [c+'0' for (c of str) ].join(''); // 'a0b0c0d0e0f0'