终止for循环的方式:break和continue
break:退出循环 continue:退出本次循环
let list = [1, 2, 3, 4] for (let i = 0; i < list.length; i++) { if (i == 1) { continue } if (i == 2) { break; } }
用return、break、continue的方式都不能终止forEach循环,return
在forEach里相当于for循环里的continue,能够退出本次循环
,可以使用try...chtch
终止foreach循环
try{ var array = ["first","second","third","fourth"]; // 执行到第3次,结束循环 array.forEach(function(item,index) { if(item == "third"){ throw new Error("EndIterative"); } console.log(item); // first second }); }catch(e){ if(e.message != "EndIterative") throw e; } // 下面的代码不影响继续执行 console.log("继续执行。。。");
·map和forEach的区别
终止map循环的方式和forEach相同
let list = [1, 2, 3, 4] try { list?.map(item => { console.log('执行'); if (item == 1) { throw new Error('stop') } }) } catch (e) { if (e.message !== 'stop') { throw e } } list?.some(item => { if (item == 1) { return true } })
可以看出,forEach和map并不适合提前终止循环的情景,可以用every()、some()代替
for…in循环主要是为了遍历对象的,break或continue可以生效
注:当for…in用来遍历数组时,遍历的结果为当前元素索引值的字符串形式
const person = { name: "111", age: 18, 1: 1, job: "student", }; for (const key in person) { if (key === "age") { break; } if (key === 'name') { continue; } }
for…of和for…in都能用break和continue结束(跳出当前)循环
我们都知道for…of只能用来遍历那些内置iterator(Array, Atring, ArrayLike, Set, Map…)或者实现了@@iterator方法的数据类型,而普通的Object并没有内置iterator
for (const val of arr) {<!--{cke_protected}{C}%3C!%2D%2D%20%2D%2D%3E--> if (val === 2) {<!--{cke_protected}{C}%3C!%2D%2D%20%2D%2D%3E--> continue; } if (val === 3) {<!--{cke_protected}{C}%3C!%2D%2D%20%2D%2D%3E--> break; } }
every():相当于且,只要有一个不满足条件,就return false,只有都满足条件才会返回true
some():相当于或,只要有一个满足条件,就return true
let list = [ { name:"aaa", age:3 }, { name:"bbb", age:4 }, { name:"ccc", age:5 }, ] var every = list.every(function (item) { return item.age > 4 }) console.log(eve) // false var some = list.some(function (item) { return item.age > 4 }) console.log(some) // true
some退出循环:return / return true(不能return false) every退出循环:return false