Calculating investment values with javascript

I am currently learning javascript. I have created a calculator to find invesment future value. It is giving me an incorrect value when it displays the future value. I have checked the formula several times but it still gives me an error. Also, I have set alerts to appear if the interest is less than 0 or greater than 20 but nothing is showing. How would i be able to properly display the correct future value and alerts when necessary? Example

Javascript

var $ = function (id) {
    return document.getElementById(id);
}

var calculate_click = function () {
    var investment = parseFloat( $("investment").value );
    var annualRate = parseFloat( $("rate").value ) /100;
    var years = parseInt( $("years").value );

    $("futureValue").value = "";

    if (isNaN(investment) || investment <= 0) {
        alert("Investment must be a valid numbernand greater than zero.");
    } else if(isNaN(annualRate) || annualRate <= 0 || annualRate > 20) {
        alert("Annual rate must be a valid numbernand less than or equal to 20.");
    } else if(isNaN(years) || years <= 0 || years > 50) {
        alert("Years must be a valid numbernand less than or equal to 50.");
    } else {
        //var monthlyRate = annualRate / 12;
        //var months = years * 12;
        var futureValue = 0;

        for ( i = 1; i <= years; i++ ) {

            futureValue = ( futureValue + investment ) *
                ( 1 + annualRate );

        }
        $("futureValue").value = futureValue.toFixed(2);
    } 
}

var clear_click = function () {
    $("investment").value = "";
    $("rate").value = "";
    $("years").value = "";
    $("futureValue").value = "";
}

window.onload = function () {
    $("calculate").onclick = calculate_click;
    $("investment").focus();
    $("clear").onclick = clear_click;
}

Answer

Using .value is incorrect, its javascript, while this is jquery, try adding a # in front and use .val() instead.

Its similar to this:

jquery function val() is not equivalent to “$(this).value=”?

EDIT

He’s not using jquery, ignore this.

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Answer