用 isNaN(Number(val) 方法判断是否为<非数字>

console.log('value1: 0')
const value1 = 0
console.log('Number(value1)', Number(value1))
console.log('isNaN(value1)', isNaN(value1))
console.log('isNaN(Number(value1)', isNaN(Number(value1)))

console.log('===============')
console.log('value2: \'0\'')
const value2 = '0'
console.log('Number(value2)', Number(value2))
console.log('isNaN(value2)', isNaN(value2))
console.log('isNaN(Number(value2)', isNaN(Number(value2)))

console.log('===============')
console.log('value3: 1.2')
const value3 = 1.2
console.log('Number(value3)', Number(value3))
console.log('isNaN(value3)', isNaN(value3))
console.log('isNaN(Number(value3)', isNaN(Number(value3)))

console.log('===============')
console.log('value4: \'1.2\'')
const value4 = '1.2'
console.log('Number(value4)', Number(value4))
console.log('isNaN(value4)', isNaN(value4))
console.log('isNaN(Number(value4)', isNaN(Number(value4)))

console.log('===============')
console.log('value5: undefined')
const value5 = undefined
console.log('Number(value5)', Number(value5))
console.log('isNaN(value5)', isNaN(value5))
console.log('isNaN(Number(value5)', isNaN(Number(value5)))

console.log('===============')
console.log('value6: null')
const value6 = null
console.log('Number(value6)', Number(value6))
console.log('isNaN(value6)', isNaN(value6))
console.log('isNaN(Number(value6)', isNaN(Number(value6)))

console.log('===============')
console.log('value7: \'\'')
const value7 = ''
console.log('Number(value7)', Number(value7))
console.log('isNaN(value7)', isNaN(value7))
console.log('isNaN(Number(value7)', isNaN(Number(value7)))

value1: 0
Number(value1) 0
isNaN(value1) false
isNaN(Number(value1) false
===============
value2: '0'
Number(value2) 0
isNaN(value2) false
isNaN(Number(value2) false
===============
value3: 1.2
Number(value3) 1.2
isNaN(value3) false
isNaN(Number(value3) false
===============
value4: '1.2'
Number(value4) 1.2
isNaN(value4) false
isNaN(Number(value4) false
===============
value5: undefined
Number(value5) NaN
isNaN(value5) true
isNaN(Number(value5) true
===============
value6: null
Number(value6) 0
isNaN(value6) false
isNaN(Number(value6) false
===============
value7: ''
Number(value7) 0
isNaN(value7) false
isNaN(Number(value7) false