1、数组常用方法
var colors = ["red", "blue", "green"]; //creates an array with three strings
alert(colors.toString()); //red,blue,green
alert(colors.valueOf()); //red,blue,green
alert(colors); //red,blue,green
2、数组map()方法
var numbers = [1,2,3,4,5,4,3,2,1];
var mapResult = numbers.map(function(item, index, array){
//item 数组元素 index元素对应索引 array原数组
console.log(array === numbers);//true
return item * 2;
});
console.log(mapResult); //[2,4,6,8,10,8,6,4,2]
3、数组reduce()方法
var values = [1,2,3,4,5];
//接收一个函数，然后从左到右遍历item，直到reduce到一个值。
var sum = values.reduce(function(prev, cur, index, array){
console.log(array === values);
console.log(index);//1,2,3,4 数组的索引从1开始
return prev + cur;//前后两个值相加
});
alert(sum);//15
4、数组concat()方法
//concat() 方法用于连接两个或多个数组。
//该方法不会改变现有的数组，而仅仅会返回被连接数组的一个副本。
//语法
//arrayObject.concat(arrayX,arrayX,......,arrayX)
var colors = ["red", "green", "blue"];
var colors2 = colors.concat("yellow", ["black", "brown"]);
alert(colors); //red,green,blue
alert(colors2); //red,green,blue,yellow,black,brown
5、数组长度length
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"
alert(colors.length);//3
alert(names.length);//1
var colors = ["red", "blue", "green"]; //creates an array with three strings
var names = []; //creates an empty array
var values = [1,2,]; //AVOID! Creates an array with 2 or 3 items
var options = [,,,,,]; //AVOID! creates an array with 5 or 6 items
alert(colors.length); //3
alert(names.length); //0
alert(values.length); //2 (FF, Safari, Opera) or 3 (IE)
alert(options.length); //5 (FF, Safari, Opera) or 6 (IE)
var colors = ["red", "blue", "green"]; //creates an array with three strings
colors.length = 2;
alert(colors[2]); //undefined
var colors = ["red", "blue", "green"]; //creates an array with three strings
colors.length = 4;
alert(colors[3]); //undefined
var colors = ["red", "blue", "green"]; //creates an array with three strings
colors[colors.length] = "black"; //add a color
colors[colors.length] = "brown"; //add another color
alert(colors.length); //5
alert(colors[3]); //black
alert(colors[4]); //brown
var colors = ["red", "blue", "green"]; //creates an array with three strings
colors[99] = "black"; //add a color (position 99)
alert(colors.length); //100
6、数组方法every和some
//every()与some()方法都是JS中数组的迭代方法。
//every()是对数组中的每一项运行给定函数，如果该函数对每一项返回true,则返回true。
//some()是对数组中每一项运行指定函数，如果该函数对任一项返回true，则返回true。
var numbers = [1,2,3,4,5,4,3,2,1];
var everyResult = numbers.every(function(item, index, array){
return (item > 2);
});
alert(everyResult); //false
var someResult = numbers.some(function(item, index, array){
return (item > 2);
});
alert(someResult); //true
7、数组filter()方法
//从数组中找到适合条件的元素（比如说大于某一个元素的值）
var numbers = [1,2,3,4,5,4,3,2,1];
var filterResult = numbers.filter(function(item, index, array){
return (item > 2);
});
alert(filterResult); //[3,4,5,4,3]
8、数组indexOf和lastIndexOf
//indexOf() 方法可返回某个指定的字符串值在字符串中首次出现的位置。
//语法
//stringObject.indexOf(searchvalue,fromindex)
//searchvalue 必需。规定需检索的字符串值。
//fromindex 可选的整数参数。规定在字符串中开始检索的位置。它的合法取值是 0 到 stringObject.length - 1。如省略该参数，则将从字符串的首字符开始检索。
var numbers = [1,2,3,4,5,4,3,2,1];
alert(numbers.indexOf(4)); //3
alert(numbers.lastIndexOf(4)); //5
alert(numbers.indexOf(4, 4)); //5
alert(numbers.lastIndexOf(4, 4)); //3
var person = { name: "Nicholas" };
var people = [{ name: "Nicholas" }];
var morePeople = [person];
alert(people.indexOf(person)); //-1
alert(morePeople.indexOf(person)); //0
9、数组toLocaleString和toString
var person1 = {
toLocaleString : function () {
return "Nikolaos";
},
toString : function() {
return "Nicholas";
}
};
var person2 = {
toLocaleString : function () {
return "Grigorios";
},
toString : function() {
return "Greg";
}
};
var people = [person1, person2];
alert(people); //Nicholas,Greg
alert(people.toString()); //Nicholas,Greg
alert(people.toLocaleString()); //Nikolaos,Grigorios
10、数组push和pop方法
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
11、数组方法unshift和shift
//unshift() 方法可向数组的开头添加一个或更多元素，并返回新的长度。
//shift() 方法用于把数组的第一个元素从其中删除，并返回第一个元素的值。
var colors = new Array(); //create an array
var count = colors.unshift("red", "green"); //push two items
alert(count); //2
count = colors.unshift("black"); //push another item on
alert(count); //3
var item = colors.pop(); //get the first item
alert(item); //"green"
alert(colors.length); //2
12、数组倒序方法reverse
var values = [1, 2, 3, 4, 5];
values.reverse();
alert(values); //5,4,3,2,1
13、数组排序方法sort
function compare(value1, value2) {
if (value1 < value2) {
return -1;
} else if (value1 > value2) {
return 1;
} else {
return 0;
}
}
var values = [0, 1, 16, 10, 15];
values.sort(compare);
alert(values); //0,1,10,15,16
//sort 改变原数组
14、数组方法slice
var colors = ["red", "green", "blue", "yellow", "purple"];
var colors2 = colors.slice(1);
var colors3 = colors.slice(1,4);
alert(colors2); //green,blue,yellow,purple
alert(colors3); //green,blue,yellow
15、数组方法splice
var colors = ["red", "green", "blue"];
var removed = colors.splice(0,1);//remove the first item
alert(colors); //green,blue
alert(removed); //red - one item array
removed = colors.splice(1, 0, "yellow", "orange"); //insert two items at position 1
alert(colors); //green,yellow,orange,blue
alert(removed); //empty array
removed = colors.splice(1, 1, "red", "purple"); //insert two values, remove one
alert(colors); //green,red,purple,orange,blue
alert(removed); //yellow - one item array
16、数组isArray()方法
alert(Array.isArray([])); //true
alert(Array.isArray({})); //false
以上就是今天的javascript学习小结，之后每天还会继续更新，希望大家继续关注。
