JSFiddle - React, Tailwind, and code Playground

JavaScript

function truncator(numToTruncate, intDecimalPlaces = 2) {    
    var numPower = Math.pow(10, intDecimalPlaces); // "numPowerConverter" might be better
    return ~~(numToTruncate * numPower)/numPower;
}

console.log('in result should been 0.29, but show 0.28');
console.log(truncator((10 * 2.9) / 100));