1、数组搜索
1.1判断数组中是否存在某个值
①indexOf
indexOf.png
②lastIndexOf
lastIndexOf.png
③includes
includes.png
④find(返回符合条件的第一个元素,,无满足返回undefined)
⑤findIndex (返回符合条件的第一个元素的位置,无满足返回-1)
⑥filter(返回符合条件的所有元素的数组,无满足元素返回空数组)
1.2 map方法
map.png
//若arr为[],map返回的也是[]
let arr = [3000, 2000, 4500, 4200, 3500, 6000, 8000];
//const result = arr.map(item => {
// return item * 2;
//})
const result = arr.map(item => item * 2)
console.log(result);//[6000, 4000, 9000, 8400, 7000, 12000,16000]
1.3reduce(累积操作)
image.png
//累加
let arr = [2, 4, 6, 8]
let result = arr.reduce((total, currentValue, currentIndex, arr) => {
console.log(total);//10 12 16 22
console.log(currentValue);//2,4,6,8
console.log(currentIndex); //0,1,2,3
console.log(arr); //[2, 4, 6, 8]
return total + currentValue;
}, 10)
console.log(result);//30
//求平均值
let result = arr.reduce((total, currentValue, currentIndex, arr) => {
total += currentValue;
if (currentIndex == arr.length - 1) {
return total / arr.length;
}
return total;
});
console.log(result);
//数组扁平化
//reduce
let arr = [
1, [1, 2],
[3, 4],
[5, 6]
]
let result = arr.reduce((total, currentValue) => total.concat(currentValue), []);
console.log(result);
//递归
function flatten(arr) {
let result = [];
for (let i = 0; i < arr.length; i++) {
if (Array.isArray(arr[i])) {
result = result.concat(flatten(arr[i]));
} else {
result.push(arr[i]);
}
}
return result;
}
console.log(flatten(arr));
//拓展运算符
unction flatten(arr) {
while (arr.some(item => {
Array.isArray(item)
})) {
return [].concat(...arr)
}
}
console.log(flatten(arr));
console.log([].concat(...arr));
//toString + split
let result2 = arr.toString();
console.log(result2.split(','));
//flat
console.log(arr.flat());
//
1.4数组排序
//升序
let arr = ["Orange", "Apple", "Grapes", "Banana"];
let arr2 = [5, 40, 3, 9, 6];
console.log(arr.sort());//[ 'Apple', 'Banana', 'Grapes', 'Orange' ]
console.log(arr2.sort());//[ 3, 40, 5, 6, 9 ]
console.log(arr2.sort((a, b) => {//[ 3, 5, 6, 9, 40
return a - b;
}));
//字母降序
//先升序再 reverse
let arr = ["Orange", "Apple", "Grapes", "Banana"];
console.log(arr2.sort().reverse());
//如果数组中有undefined,undefined排在最后
//对象排序
//对象排序
const employess = [
{ eNo: 1001, salary: 3000 },
{ eNo: 1002, salary: 2200 },
{ eNo: 1003, salary: 3400 },
{ eNo: 1004, salary: 5000 },
]
employess.sort((a, b) => {
return a.salary - b.salary
})
console.log(employess);
//[
//{ eNo: 1002, salary: 2200 },
//{ eNo: 1001, salary: 3000 },
//{ eNo: 1003, salary: 3400 },
//{ eNo: 1004, salary: 5000 }
//]
1.5数组解构
let arr = [1,2,3,4];
let [a,b,c,d] = arr;
console.log(a,b,c,d);//1 2 3 4
//不完全结构
let arr = [1,2,3,4];
let [a,,c,d] = arr;
console.log(a,,c,d); // 1 3 4
//值交换
let a = 4;
let b = 5;
let [a,b] = let [b,a]
//与拓展运算符一起使用
let arr = [4, 5, 6];
let [a, ...b] = arr;
console.log(a);
console.log(b);
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