Access Control Request Headers, is added to header in AJAX request with jQuery

What you saw in Firefox was not the actual request; note that the HTTP method is OPTIONS, not POST. It was actually the ‘pre-flight’ request that the browser makes to determine whether a cross-domain AJAX request should be allowed: http://www.w3.org/TR/cors/ The Access-Control-Request-Headers header in the pre-flight request includes the list of headers in the actual … Read more

Palindrome check in Javascript

Maybe I will suggest alternative solution: UPD. Keep in mind however that this is pretty much “cheating” approach, a demonstration of smart usage of language features, but not the most practical algorithm (time O(n), space O(n)). For real life application or coding interview you should definitely use loop solution. The one posted by Jason Sebring in this … Read more

node.js TypeError: path must be absolute or specify root to res.sendFile [failed to parse JSON]

The error is pretty clear, you need to specify an absolute (instead of relative) path and/or set root in the config object for res.sendFile(). Examples: or specify a root (which is used as the base path for the first argument to res.sendFile(): Specifying the root path is more useful when you’re passing a user-generated file path which could potentially contain malformed/malicious … Read more

Proper way to wait for one function to finish before continuing?

One way to deal with asynchronous work like this is to use a callback function, eg: As per @Janaka Pushpakumara’s suggestion, you can now use arrow functions to achieve the same thing. For example: firstFunction(() => console.log(‘huzzah, I\’m done!’)) Update: I answered this quite some time ago, and really want to update it. While callbacks are … Read more

JavaScript innerHTML not updating element

The element doesn’t exist at the time you’re attempting to set a value. You need to call this after the <h1> has been added to the DOM. You can either move this <script> tag down further, or add your logic to a function which ought to be called when the document has been loaded: Demo: http://jsfiddle.net/Lr2Hm/

When is JavaScript synchronous?

JavaScript is always synchronous and single-threaded. If you’re executing a JavaScript block of code on a page then no other JavaScript on that page will currently be executed. JavaScript is only asynchronous in the sense that it can make, for example, Ajax calls. The Ajax call will stop executing and other code will be able to … Read more