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

如果数组的元素是数值，可以用两数相减，就能排序

function compare(value1, value2){ return value2 - value1; 
}let  values = [2,4,1,3,6,5]
values.sort(compare)
console.log(values) //[6,5,4,3,2,1]function compare(value1, value2){ return value1 - value2; 
}let  values = [2,4,1,3,6,5]
values.sort(compare)
console.log(values) //[1,2,3,4,5,6]

操作方法

concat()

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

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

let colors = ["red", "green", "blue"]; //删除
let removed = colors.splice(0,1); // 删除第一项
alert(colors); // green,blue 
alert(removed); // red，只有一个元素的数组//插入
removed = colors.splice(1, 0, "yellow", "orange"); // 在位置 1 插入两个元素
alert(colors); // green,yellow,orange,blue 
alert(removed); // 空数组//替换
removed = colors.splice(1, 1, "red", "purple"); // 插入两个值，删除一个元素
alert(colors); // green,red,purple,orange,blue 
alert(removed); // yellow，只有一个元素的数组

搜索和位置方法

 严格相等

• indexOf()、lastIndexOf()和 includes()。这三个方法都可以用来判断当前数组是否存在某个值
• indexOf()和 lastIndexOf()都返回要查找的元素在数组中的位置，如果没找到则返回-1。
• includes()返回布尔值（includes是es7新增属性）
• 这些方法都接收两个参数：要查找的元素和一个可选的起始搜索位置。

let numbers = [1, 2, 3, 4, 5, 4, 3, 2, 1]; 
alert(numbers.indexOf(4)); // 3 
alert(numbers.indexOf(4, 4)); // 5 alert(numbers.lastIndexOf(4)); // 5 
alert(numbers.lastIndexOf(4, 4)); // 3 alert(numbers.includes(4)); // true 
alert(numbers.includes(4, 7)); // false //对象数组let person = { name: "Nicholas" }; 
let people = [{ name: "Nicholas" }]; 
let morePeople = [person]; alert(people.indexOf(person)); // -1 
alert(morePeople.indexOf(person)); // 0 
alert(people.includes(person)); // false 
alert(morePeople.includes(person)); // true

断言函数

• 断言函数接收 3 个参数：元素、索引和数组本身。
• 其中元素是数组中当前搜索的元素，索引是当前元素的索引，而数组就是正在搜索的数组。
• 断言函数返回真值，表示是否匹配。
• 找到匹配项后，这两个方法都不再继续搜索

find（）

返回第一个匹配的元素

 const people = [{ name: "Matt", age: 27 }, { name: "Nicholas", age: 29 } ,{ name: "Jerry", age: 26} 
]; 
console.log(people.find((element, index, array) => element.age < 28)); 
// {name: "Matt", age: 27}

findIndex()

返回第一个匹配元素的索引。

 const people = [{ name: "Matt", age: 27 }, { name: "Nicholas", age: 29 } ,{ name: "Jerry", age: 26} 
]; 
console.log(people.findIndex((element, index, array) => element.age < 28)); 
//0

迭代方法

• ECMAScript 为数组定义了 5 个迭代方法
• 每个方法接收两个参数
• 这些方法都不改变调用它们的数组。

every()

let numbers = [1, 2, 3, 4, 5, 4, 3, 2, 1]; 
let everyResult = numbers.every((item, index, array) => item > 2); 
console.log(everyResult); // false

let numbers = [1, 2, 3, 4, 5, 4, 3, 2, 1]; 
let everyResult = numbers.some((item, index, array) => item > 2); 
console.log(everyResult); // true

let numbers = [1, 2, 3, 4, 5, 4, 3, 2, 1]; 
let filterResult = numbers.filter((item, index, array) => item > 2); 
console.log(filterResult); //[ 3,4,5,4,3]

let newarr =[]
let numbers = [1, 2, 3, 4, 5, 4, 3, 2, 1]; 
numbers.forEach((item, index, array) => { // 执行某些操作 
item += 1newarr.push(item)
});
console.log(numbers) //[1,2,3,4,5,4,3,2,1]
console.log(newarr) // [2,3,4,5,6,5,4,3,2]

let numbers = [1, 2, 3, 4, 5, 4, 3, 2, 1]; 
let mapResult = numbers.map((item, index, array) => item * 2);console.log(mapResult) // [2, 4, 6, 8, 10, 8, 6, 4, 2]; 
console.log(numbers)   // [1, 2, 3, 4, 5, 4, 3, 2, 1]; 

let values = [1, 2, 3, 4, 5]; 
let sum = values.reduce((prev, cur, index, array) => prev + cur); 
console.log(sum); // 15