let  num1 = 80000000000;
console.log(typeof num1); //number
console.log(num1.toPrecision(1)); //8e+10
console.log(typeof num1.toPrecision(1));//string

let num2 = 99;
//代表的是有多少位数
console.log(num2.toPrecision(1));//1e+2
console.log(num2.toPrecision(2));//99
console.log(num2.toPrecision(3));//99.0
console.log(num2.toPrecision(8));//99.000000