Javascript(学习)

Question

我正在从“JavaScript 圣经”一书中学习 javascript，但我遇到了一些困难。我试图理解这段代码:

function checkIt(evt) {
    evt = (evt) ? evt : window.event
    var charCode = (evt.which) ? evt.which : evt.keyCode
    if (charCode > 31 && (charCode < 48 || charCode > 57)) {
        status = "This field accept only numbers."
        return false
    }
    status = ""
    return true
}

谁能给我解释一下？

Answer 1

我假设您只是想让我们解释代码的作用。如果是这样，请参见下文:

// Create a function named checkIt, which takes an argument evt.
function checkIt(evt) {

    // If the user has passed something in the argument evt, take it.
    // Else, take the window.event as evt.
    evt = (evt) ? evt : window.event;

    // Get the Character Code. It can be either from evt.which or evt.keyCode,
    // depending on the browser.
    var charCode = (evt.which) ? evt.which : evt.keyCode;

    // If the Character is not a number, the do not allow the user to type in.
    // The reason for giving 31 to 48 and greater than 57 is because, each key
    // you type has its own unique character code. From 31 to 48, are the numeric
    // keys in the keyboard.
    if (charCode > 31 && (charCode < 48 || charCode > 57)) {

        // Give a status informing the user.
        status = "This field accept only numbers.";

        // Prevent the default action of entering the character.
        return false;
    }

    // Clear the status
    status = "";

    // Allow the user to enter text.
    return true;
}

ASCII码引用

_{(来源:cdrummond.qc.ca)}

_{(来源:cdrummond.qc.ca)}

PS:我编辑了您的代码，添加了分号 ;，但分号丢失了。