Verifying user input in JavaScript

This javascript library contains functions for verifying the contents of a text box. For each function the name of a text box is passed as input, along with any restrictions on the contents. If the contents of the box are not legal, a warning is displayed.

function verifyNum(textBox)
    // Assumes: textBox is a text box in the page
    // Results: warns if box contents is not a number
    {
        var boxValue;

        boxValue = parseFloat(textBox.value);
        if ( isNaN(boxValue) ) {
            alert("You must enter a number value!");
        }
    }

    function verifyNumInRange(textBox, low, high)
    // Assumes: textBox is a text box in the page, low <= high
    // Results: warns if box contents is not a number in range low..high
    {
        var boxValue;

        boxValue = parseFloat(textBox.value);
        if ( isNaN(boxValue) || (boxValue < low) || (boxValue > high)) {
            alert("You must enter a number value in the range [" +
                  low + ".." + high + "]");
        }
    }

    function verifyInt(textBox)
    // Assumes: textBox is a text box in the page
    // Results: warns if box contents is not an integer
    {
        var boxValue;

        boxValue = parseFloat(textBox.value);
        if ( isNaN(boxValue) || (boxValue % 1 != 0) ) {
            alert("You must enter an integer value!");
        }
    }

    function verifyIntInRange(textBox, low, high)
    // Assumes: textBox is a text box in the page, low <= high
    // Results: warns if box contents is not an integer in range low..high
    {
        var boxValue;

        boxValue = parseFloat(textBox.value);
        if ( isNaN(boxValue) || (boxValue % 1 != 0) ||
                                (boxValue < low)    || 
                                (boxValue > high)) {
            alert("You must enter an integer value in the range [" +
                  low + ".." + high + "]");
        }
    }

    function verifyOneOf(textBox, options)
    // Assumes: textBox is a text box in the page, options is a list
    // Results: warns if box contents is not one of the options
    {
        for (i = 0; i < options.length; i++) {
            if (textBox.value == options[i]) {
                return;
            }
        }
        
        alert("You must enter one of the following: " + options);
    }