如果你的源代码是typescript，你可以使用这样的函数:

public static ToFixedRounded(decimalNumber: number, fractionDigits: number): number {
    var rounded = Math.pow(10, fractionDigits);
    return (Math.round(decimalNumber * rounded) / rounded).toFixed(fractionDigits) as unknown as number;
}

const solds = 136780000000; 
const number = (solds >= 1000000000 && solds < 1000000000000) ? { divisor: 1000000000, postfix: "B" }: (solds >= 1000000 && solds < 1000000000) ? { divisor: 1000000, postfix: "M" }: (solds >= 1000 && solds < 1000000) ? { divisor: 1000, postfix: "K" }: { divisor: 1, postfix: null }; 
const floor = Math.floor(solds / number.divisor).toLocaleString(); 
const firstDecimalIndex = solds.toLocaleString().charAt(floor.length+1); 
const final =firstDecimalIndex.match("0")? floor + number.postfix: floor + "." + firstDecimalIndex + number.postfix; 
console.log(final);

136780000000 --> 136.7B

1367800 --> 1.3M

1342 --> 1.3K

数学。Round (num * 10) / 10工作，这里是一个例子…

var number = 12.3456789
var rounded = Math.round(number * 10) / 10
// rounded is 12.3

如果你想让它有一个小数点，即使它是0，然后加…

var fixed = rounded.toFixed(1)
// fixed is always to 1 d.p.
// NOTE: .toFixed() returns a string!

// To convert back to number format
parseFloat(number.toFixed(2))
// 12.34
// but that will not retain any trailing zeros

// So, just make sure it is the last step before output,
// and use a number format during calculations!

编辑:添加圆与精度功能…

使用这个原理，作为参考，这里有一个方便的小圆函数，它需要精度…

function round(value, precision) {
    var multiplier = Math.pow(10, precision || 0);
    return Math.round(value * multiplier) / multiplier;
}

．.． 使用……

round(12345.6789, 2) // 12345.68
round(12345.6789, 1) // 12345.7

．.． 默认舍入到最接近的整数(精度为0)…

round(12345.6789) // 12346

．.． 可以四舍五入到最接近的10或100等…

round(12345.6789, -1) // 12350
round(12345.6789, -2) // 12300

．.． 正确处理负数……

round(-123.45, 1) // -123.4
round(123.45, 1) // 123.5

．.． 并且可以与toFixed结合使用，以一致的格式作为字符串…

round(456.7, 2).toFixed(2) // "456.70"

var number = 123.456;

console.log(number.toFixed(1)); // should round to 123.5

数学。整数(num * 10) / 10无效。

例如，1455581777.8-145558160.4会得到1310023617.3999999。

所以只使用num。tofixed (1)

function rnd(v,n=2) {
    return Math.round((v+Number.EPSILON)*Math.pow(10,n))/Math.pow(10,n)
}

这个很好地抓住了极端情况