手写foreach、filter、map、every、some函数

1.foreach实现原理

function foreach(array, fn) {
    for (i = 0; i < array.length; i++) {
        fn(array[i])
    }
}
// 测试
let arr = [1,2,5,6,7,8];
foreach(arr,function(item){
    console.log(item)
})

2.filter实现原理

function filter(array, fn) {
    let results = []
    for (i = 0; i < array.length; i++) {
        if (fn(array[i])) {
            results.push(array[i])
        }
    }
    return results;
}
// 测试 过滤偶数
let arr = [1, 2, 5, 6, 7, 8];
let r = filter(arr, function (item) {
    return item % 2 === 0
})
console.log(r)

3.map实现原理

const map = (array,fn)=>{
 let results = []
 for(let value of array){
    results.push(fn(value))
 }
 return results;
}
// 测试
let arr = [1,2,3,4,5]
let r = map(arr,v=>v*v)
console.log(r)

4.every实现原理

const every = (array, fn) => {
   let result = true
   for (let value of array) {
      result = fn(value)
      if (!result) {
         break
      }
   }
   return result;
}
// 测试
let arr = [1, 2, 3, 4, 5]
let r = every(arr, v => v > 0)
console.log(r)

5.some实现原理

const some = (array, fn) => {
   let result = true
   for (let value of array) {
      result = fn(value)
      if (result) {
         break
      }
   }
   return result;
}
// 测试
let arr = [2, 3, 4, 5, 6, 1]
let r = some(arr, v => v % 2 === 0)
console.log("输出结果:"+r)

以上函数主要利用了函数可以作为参数这一特性来实现的。