js 保留两位小数不四舍五入

function customToFixed(num: string, len: number = 2) {
    num = num.toString()
    let index = num.indexOf('.')
    if (index !== -1) {
        num = num.substring(0, index + 1 + len)
    } else {
        num = num.substring(0)
    }
    return parseFloat(num).toFixed(len)
}