利用取模来判断后面0.5来去最近值

const readline = require('readline')
const r = readline.createInterface({
    input: process.stdin,
    ouput: process.stdout
})

r.on('line', (line)=>{
    const value = (parseFloat(line) * 10) % 10
    if (value >= 5) {
        console.log(Math.ceil(line))
    } else {
        console.log(Math.floor(line))
    }
})

还有一种最简单的就是+0.5向下取值

const readline = require('readline')
const r = readline.createInterface({
    input: process.stdin,
    ouput: process.stdout
})

r.on('line', (line)=>{
    console.log(Math.floor(line*1 + 0.5))
})