Javascript 数组（Array）相关内容总结

var colors = new Array(); //创建新数组
var num = new Array(3); //创建包含三项的新数组
var names = new Array("Dalu"); // 创建包含一项数据“Dalu”的新数组

if(Array.isArray(value)){
// ECMAscript5新增
// 是数组
};

if(value instanceof Array){
// 是数组
}

var nums = [1,2,3];
alert(nums.toString());  // ”1,2,3”
alert(nums.join(’||’);  // “1||2||3”

// 栈方法

var colors = new Array();
var count = colors.push("red","green");  //在最后面推入两项
console.log(colors);  //["red","green"]
console.log(count);  //计数为2

count = colors.push("black");  //在最后面推入另一项
console.log(count);  //3

var item = colors.shift();  //移除数组中的第一个项并返回该项
console.log(item);  //"red"
console.log(colors.length); //2

// 队列方法

var colors = new Array();
var count = colors.unshift("red","green");  //在最前面推入两项
console.log(count);  //2

count = colors.unshift("black");  //在最前面推入另一项
console.log(count);  //3

var item = colors.pop();  //移除数组中的最后一项并返回该项
console.log(item);  //"green"
console.log(corlors.length); //2

// reverse() 反转数组项的顺序

var values = [1,2,3,4,5];
values.reverse();
console.log(values);  // [5,4,3,2,1]

// sort() 调用每个数组项的toString()转型方法，然后比较得到的字符串，以确定如何排序

var values = [0,1,5,10,15];
values.sort();
console.log(values);  // [0,1,10,15,5]

// sort()方法可以接收一个比较函数作为参数，以便我们指定哪个值位于哪个值的前面。
/* 比较函数接收两个参数，如果第一个参数应该位于第二个之前则返回一个负数，如果两个参数相等则返回0，如果第一个参数应该位于第二个之后则返回一个正数。以下就是一个简单的比较函数：*/

// 升序
function compare(value1,value2){
　　if(value1 < value2){
　　　　return -1;
　　} else if(value1 > value2){
　　　　return 1;
　　} else {
　　　　return 0;
　　}
}
var values = [0,1,5,10,15];
values.sort(compare);
console.log(values);  // [0,1,5,10,15]

// 降序
function compare(value1,value2){
　　if(value1 < value2){
　　　　return 1;
　　} else if(value1 > value2){
　　　　return -1;
　　} else {
　　　　return 0;
　　}
}
var values = [0,1,5,10,15];
values.sort(compare);
console.log(values);  // [15,10,5,1,0]

/*对于数值类型或者其valueOf()方法会返回数值类型的对象类型，可以使用一个更简单的比较函数。这个函数只要用第二个值减第一个值即可*/
function compare(value1,value2){
　　return value2 - value1;
}

// concat()

var colors = ["red","green","blue"];
var colors2 = colors.concat("yellow",["black","brown"]);
console.log("colors");  //["red","green","blue"]
console.log("colors2"); //["red","green","blue","yellow","black","brown"]

// slice()

var colors = ["red","green","blue","yellow","purole"];
var colors2 = colors.slice(1);
var colors3 = colors.slice(1,4);
console.log(colors2)  //["green","blue","yellow","purole"]
console.log(colors3)  //["green","blue","yellow"]

// splice()

var colors = ["red","green","blue"];
var removed = colors.splice(0,1);  // 删除第一项
console.log(colors);  //["green","blue"]
console.log(removed); //["red"]，返回的数组只包含一项

removed = colors.splice(1,0,"yellow","orange"); //从位置1开始插入两项
console.log(colors);  //["green","yellow","orange","blue"]
console.log(removed); //返回一个空数组[]

removed = colors.splice(1,2,"red","purple");    //插入两项，删除两项
console.log(colors);  //["green","red","purple","blue"]
console.log(removed); //["yellow"，"orange"]，返回类型为Array，包含两项

// indexOf()

var numbers = [1,2,3,4,5,4,3,2,1];
console.log(numbers.indexOf(4));       //3
console.log(numbers.lastIndexOf(4));   //5
console.log(numbers.indexOf(4,4));     //5
console.log(numbers.lastIndexOf(4,4))  //3

var person = {name:"Dalu"};
var people = [{name:"Dalu"}];
var morePeople = [person];
console.log(people.indexOf(person));     //-1
console.log(morePeople.indexOf(person)); //0

// every()

var numbers = [1,2,3,4,5,4,3,2,1];
var everyResult = numbers.every(function(item,index,array){
    return (item > 2);
});
console.log(everyResult);  //false
var someResult = numbers.some(function(item,index,array){
    return (item > 2);
});
console.log(someResult);   //ture

// filter()

var numbers = [1,2,3,4,5,4,3,2,1];
var filterResult = numbers.filter(function(item,index,array){
    return (item > 2);
});
console.log(filterResult); //[3,4,5,4,3]

// map()

var numbers = [1,2,3,4,5,4,3,2,1];
var mapResult = numbers.map(function(item,index,array){
    return item * 2;
});
console.log(mapResult);    //[2,4,6,8,10,8,6,4,2]

// forEach()

var numbers = [1,2,3,4,5,4,3,2,1];
numbers.forEach(function(item,index,array){
    console.log("item:" + item)   //返回当前项的值
    console.log("index:" + index) //返回当前项的索引
    console.log("array:" + array) //返回数组的字符串1,2,3,4,5,4,3,2,1
});

// reduce()

var values = [1,2,3,4,5];
var sum = values.reduce(function(prev,cur,index,array){
    return prev + cur;
});
console.log(sum); //15

// reduceRight() 倒序

var value = [1,2,3,4,5];
var sum = values.reduceRight(function(prev,cur,index,array){
    return prve + cur;
});
console.log(sum); //15 由于都是累计相加，所以结果一样