js NaN, null, undefined judgment, judging whether the attributes of a row in the array are all null values (filtering blank rows), judging whether the attributes in the object are all null values

1. Determine whether NaN (NaN (not a number) belongs to the Number type)

isNaN (the field that needs to be judged)

2. Determine whether it is undefined (field is undefined)

typeof (field to be judged) == "undefined"

3. Determine whether it is null (the field is defined but has no value)

function isNull(value) {
        if (value === null) { // 是三等号操作符（===）而不是双等号
            return true;
        } else {
            return false;
        }
    }

Method Two:

function isNull(value) {
        if (!value && typeof value != "undefined" && value != 0) {
            return true;
        } else {
            return false;
        }
    }
typeof 参数 != "undefined" 排除了 undefined；
参数 != 0 排除了数字零和 false。

4. Determine whether the attributes of a row in the array are all null values ​​(filter blank rows), and determine whether the attributes in the object are all null values

data.forEach((v,i) => {
        if (i>0) {
          const keys = Object.keys(v)
          const allNull = Object.values(v).filter(obj=> obj=='') // 判断一行中是否每个属性都是空数据, 过滤空行
          // console.log('allNull', allNull, allNull.length, keys.length, keys);
          if (allNull.length !== keys.length) { // 一行中所有属性都是空值
            console.log('一行中所有属性都是空值')
          }
        }
      })