JS基础知识（数组）

1，数组

var colors = new Array();
var colors = new Array(20);
var colors = new Array(“red”, “blue”, “green”);
var colors = new Array(3); //create an array with three items
var names = new Array(“Greg”); //create an array with one item, the string “Greg”

shift：删除原数组第一项，并返回删除元素的值；如果数组为空则返回undefined

var a = [1,2,3,4,5];
var b = a.shift(); //a：[2,3,4,5]   b：1

unshift：将参数添加到原数组开头，并返回数组的长度

var a = [1,2,3,4,5];
var b = a.unshift(-2,-1); //a：[-2,-1,1,2,3,4,5]   b：7

pop：删除原数组最后一项，并返回删除元素的值；如果数组为空则返回undefined

var a = [1,2,3,4,5];
var b = a.pop(); //a：[1,2,3,4]   b：5//不用返回的话直接调用就可以了

push：将参数添加到原数组末尾，并返回数组的长度

var a = [1,2,3,4,5];
var b = a.push(6,7); //a：[1,2,3,4,5,6,7]   b：7

concat：返回一个新数组，是将参数添加到原数组中构成的

var a = [1,2,3,4,5];
var b = a.concat(6,7); //a：[1,2,3,4,5]   b：[1,2,3,4,5,6,7]

放值：

var colors = [“red”, “blue”, “green”]; //define an array of strings
alert(colors[0]); //display the first item
colors[2] = “black”; //change the third item
colors[3] = “brown”; //add a fourth item

在最后面加值：

var colors = [“red”, “blue”, “green”]; //creates an array with three strings
colors[colors.length] = “black”; //add a color (position 3)
colors[colors.length] = “brown”; //add another color (position 4)

注意：

数组最多能放4,294,967,295个元素

last-in-fi rst-out (LIFO)结构：

var colors = new Array(); //create an array
var count = colors.push(“red”, “green”); //push two items
alert(count); //2
count = colors.push(“black”); //push another item on
alert(count); //3
var item = colors.pop(); //get the last item
alert(item); //”black”
alert(colors.length); //2