JS对像和数组的遍历

Posted 2020-10-28 ninalei

零. 通用遍历方法

0.1 for...in...

let obj = {0:"a", 1:"b", 2:"c"};
for (let key in obj) {
  console.log(obj[key])  
}

0.2 for...of...

let obj = {0:"a", 1:"b", 2:"c"};
for (let value of obj) {
  console.log(value)  
}

 

 

一. JS遍历对象

1.1 Object.keys()遍历

let obj = {0:"a", 1:"b", 2:"c"};
Object.keys(obj).forEach((key) => {
   console.log(key, obj[key]);
});

1.2 Object.values()遍历

let obj = {0:"a", 1:"b", 2:"c"};
Object.values(obj).forEach((value, key) => {
   console.log(key, value);
});

1.3 Object.entries()遍历

let obj = {0:"a", 1:"b", 2:"c"};
Object.entries(obj).forEach((value, key) => {
   console.log(key, value);
});

1.4 Object.getOwnPropertyNames()

let obj = {0:"a", 1:"b", 2:"c"};
Object.getOwnPropertyNames(obj);

二. JS遍历数组

2.1 forEach语句

let arr = [1, 2, 3]
arr.forEach((item) => {
   console.log(item) 
})

2.2 map方法

map不会改变原数组，callback执行返回的值会形成一个新的数组。

let arr = [1, 2, 3]
let newArr = arr.map((item) => {
   item * 2
})

 

2.3 filter方法

filter将返回值为true的元素创建一个新数组。

let arr = [1, 2, 3]
let newArr = arr.filter((item) => {
   item > 2
})

 

2.4 every方法

every，全部满足则返回true

let arr = [1, 2, 3]
let res = arr.every((item) => {
   item > 2
}) //false

 

2.5 some方法

some，只有有一项满足则返回true

let arr = [1, 2, 3]
let res = arr.some((item) => {
   item > 2
}) //true