12.20---02转换布尔值

var num1 = 100
var num2 = 0
var num3 =-1
console.log(num1, '-->', Boolean(num1)) 
console.log(num2, '-->', Boolean(num2)) 
console.log(num3, '-->', Boolean(num3)) 



var str1 = ''
var str2 = ' '
var str3 = 'abc'
console.log(str1, '-->', Boolean(str1))
console.log(str2, '-->', Boolean(str2))
console.log(str3, '-->', Boolean(str3))




var und = undefined
var nul = null
console.log(und, '-->', Boolean(und))
console.log(nul, '-->', Boolean(nul))