javascript - Read For Learn

Error: Can’t set headers after they are sent to the client

The res object in Express is a subclass of Node.js’s http.ServerResponse (read the http.js source). You are allowed to call res.setHeader(name, value) as often as you want until you call res.writeHead(statusCode). After writeHead, the headers are baked in and you can only call res.write(data), and finally res.end(data). The error “Error: Can’t set headers after they are sent.” means that you’re already in the Body or Finished … Read more

What is this JavaScript “require”?

So what is this “require?” require() is not part of the standard JavaScript API. But in Node.js, it’s a built-in function with a special purpose: to load modules. Modules are a way to split an application into separate files instead of having all of your application in one file. This concept is also present in other languages … Read more

window.onload vs document.onload

When do they fire? window.onload By default, it is fired when the entire page loads, including its content (images, CSS, scripts, etc.). In some browsers it now takes over the role of document.onload and fires when the DOM is ready as well. document.onload It is called when the DOM is ready which can be prior to images and other external content … Read more

Client on Node.js: Uncaught ReferenceError: require is not defined

This is because require() does not exist in the browser/client-side JavaScript. Now you’re going to have to make some choices about your client-side JavaScript script management. You have three options: Use the <script> tag. Use a CommonJS implementation. It has synchronous dependencies like Node.js Use an asynchronous module definition (AMD) implementation. CommonJS client side-implementations include (most of them require a build step before you … Read more

require is not defined? Node.js

In the terminal, you are running the node application and it is running your script. That is a very different execution environment than directly running your script in the browser. While the Javascript language is largely the same (both V8 if you’re running the Chrome browser), the rest of the execution environment such as libraries … Read more

JavaScript error (Uncaught SyntaxError: Unexpected end of input)

Add a second });. When properly indented, your code reads You never closed the outer $(function() {.

Is it possible to sandbox JavaScript running in the browser?

I’m wondering if it’s possible to sandbox JavaScript running in the browser to prevent access to features that are normally available to JavaScript code running in an HTML page. For example, let’s say I want to provide a JavaScript API for end users to let them define event handlers to be run when “interesting events” … Read more

How to pop an alert message box using PHP?

You could use Javascript:

Cannot read property ‘push’ of undefined when combining arrays

You get the error because order[1] is undefined. That error message means that somewhere in your code, an attempt is being made to access a property with some name (here it’s “push”), but instead of an object, the base for the reference is actually undefined. Thus, to find the problem, you’d look for code that … Read more

JQuery – $ is not defined

That error can only be caused by one of three things: Your JavaScript file is not being properly loaded into your page You have a botched version of jQuery. This could happen because someone edited the core file, or a plugin may have overwritten the $ variable. You have JavaScript running before the page is … Read more

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