JS基础知识(数组)总结

无情 阅读:207 2021-05-02 15:06:06 评论:0

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

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