JavaScript のループ ステートメントにはどのような種類がありますか?

for([初始值表达式]；[条件表达式]；[增量表达式]){
   循环体语句；
}

     var sum = 0;
     for(var i = 1; i <= 100;i++){        //在for语句中使用var声明循环变量，使代码更简洁
         sum += i;
     }
     alert("1～100的累加和sum=" + sum);

var a = [1, 2, ,,,,,,true,,,,,,, "a",,,,,,,,,,,,,,,4,,,,,56,,,,,,"b"];  //定义数组
var b = [], num = 0;
for (var i = 0; i < a.length; i ++) {  //遍历数组
    if (typeof a[i] == "number")  //如果为数字，则返回该元素的值
        b.push(a[i]);
    num ++;  //计数器
}
console.log(num);  //返回42，说明循环了42次
console.log(b);  //返回[1,2,4,56]

while 语句的基本语法如下：
while(条件表达式){
     循环体;
}

var i=1,s=0;
whiel(i<=5){
    s+=i;      
}

     var sum = 1, i = 1;
     var ex = 1;
     while(sum <= 1.5){
         sum += 1/((i + 1)*(i + 1));
         if(sum > 1.5)
              break;
         i++;
         ex +=" + 1/(" + i + "*" + i + ")";
     }
     alert("表达式的值小于等于1.5时的i=" + i + "，对应的表达式为：" + ex);

do{
  循环体;
}while (条件表达式);

     var sum = 1, i = 1;
     var ex = 1;
     do{
         sum += 1/((i + 1)*(i + 1));
         if(sum > 1.5)
              break;
         i++;
         ex +=" + 1/(" + i + "*" + i + ")";
     }while(sum <= 1.5);
     alert("表达式的值小于等于1.5时的i=" + i + "，对应的表达式为：" + ex);

let arrObj = [{
    id: 1,
    name: 'xiaohua'
},{
    id:2,
    name: 'xiaomin'
},{
    id:3,
    name: 'xiaobai'
}]
arrObj.forEach((item,index,arr)=>{
    console.log(arr) // arrObj
    console.log(index)  // 0 1 2
    console.log(item.name) // xiaohua xiaomin xiaobai
})

let arr = [1,2,3,4,5]
let arr2 = arr.map((n)=>{
      return n+1
})
console.log(arr2) // [2,3,4,5,6]
console.log(arr) // [1,2,3,4,5]

let arrObj = [{
    id: 1,
    name: 'xiaohua'
},{
    id:2,
    name: 'xiaomin'
},{
    id:3,
    name: 'xiaobai'
}]
arrObj.map((item,index,arr)=>{
    console.log(arr) // arrObj
    console.log(index)  // 0 1 2
    console.log(item.name) // xiaohua xiaomin xiaobai
})

let arrObj = [{
    id: 1,
    name: 'xiaohua'
},{
    id:2,
    name: 'xiaomin'
},{
    id:3,
    name: 'xiaobai'
}]
let arr2 = arrObj.filter((item,index,arr)=>{
    return (item.name === 'xiaohua')
})
console.log(arr2)  // [{id:1,name:'xiaohua}]

let arr = [3, 4, 5, 2, 3, undefined, null, 0, ""];
let arrNew = arr.filter(Boolean);
console.log(arrNew)  //  [3, 4, 5, 2, 3]

let obj = {name: 'xiaohua', sex: 'male', age: '28'}
console.log(Object.keys(obj))
// ["name", "sex", "age"]