数组循环及中断循环

for循环

1. 使用break,可以中断循环

let arr = [1,2,3,4,5,6,7,8,9]
for(let i = 0; i< arr.length; i++){
  if(i === 5){
    break;
  }
  console.log(arr[i])
}

2. 使用continue，循环可以继续

let arr = [1,2,3,4,5,6,7,8,9]
for(let i = 0; i< arr.length; i++){
  if(i === 5){
    continue;
  }
  console.log(arr[i])
}

3. 使用return，会报错

let arr = [1,2,3,4,5,6,7,8,9]
for(let i = 0; i< arr.length; i++){
  if(i === 5){
    return;
  }
  console.log(arr[i])
}

for...in 循环

1. 使用break,可以跳出循环

let arr = [1,2,3,4,5,6,7,8,9]
for(let i in arr){
  if(i == 5){
    break;
  }
  console.log(arr[i])
}

2. 使用continue

let arr = [1,2,3,4,5,6,7,8,9]
for(let i in arr){
  if(i == 5){
    continue;
  }
  console.log(arr[i])
}

3. 使用return，报错

let arr = [1,2,3,4,5,6,7,8,9]
for(let i in arr){
  if(i == 5){
    return;
  }
  console.log(arr[i])
}

for...of循环

1. 使用break，

let arr = [1,2,3,4,5,6,7,8,9]
for(let item of arr){
  if(item == 5){
    break;
  }
  console.log(item)
}

2. 使用continue,会跳出当前循环继续循环

let arr = [1,2,3,4,5,6,7,8,9]
for(let item of arr){
  if(item === 5){
   continue;
  }
  console.log(item)
}

3. return ,报错

let arr = [1,2,3,4,5,6,7,8,9]
for(let item of arr){
  if(item == 5){
    return;
  }
  console.log(item)
}

forEach

1. 使用break，报错

let arr = [1,2,3,4,5,6,7,8,9]
arr.forEach((item) => {
  if(5 === item){
    break;
  }
  console.log(item)
})

2. 使用continue，报错

let arr = [1,2,3,4,5,6,7,8,9]
arr.forEach((item) => {
  if(5 === item){
    continue;
  }
  console.log(item)
})

3. 使用return会跳出当前循环，但不会终止循环

let arr = [1,2,3,4,5,6,7,8,9]
arr.forEach((item) => {
  if(5 === item){
    return;
  }
  console.log(item)
})

filter

1. 使用break，报错

let arr = [1,2,3,4,5,6,7,8,9]
let result = []
result = arr.filter((item) => {
  if(5 === item){
    break;
  }
  return item
})
console.log(result)

2. 使用continue，报错

let arr = [1,2,3,4,5,6,7,8,9]
let result = []
result = arr.filter((item) => {
  if(5 === item){
    continue;
  }
  return item
})
console.log(result)

3. 使用break，会跳出当前循环，继续

let arr = [1,2,3,4,5,6,7,8,9]
let result = []
result = arr.filter((item) => {
  if(5 === item){
    return;
  }
  return item
})
console.log(result)

map

1. 使用break，报错

let arr = [1,2,3,4,5,6,7,8,9]
let result = []
result = arr.map((item) => {
  if(5 === item){
    break;
  }
  return item
})
console.log(result)

2. 使用continue，报错

let arr = [1,2,3,4,5,6,7,8,9]
let result = []
result = arr.map((item) => {
  if(5 === item){
    continue;
  }
  return item
})
console.log(result)

3. 使用return，不会报错

let arr = [1,2,3,4,5,6,7,8,9]
let result = []
result = arr.map((item) => {
  if(5 === item){
    return;
  }
  return item
})
console.log(result)