Error Checking Javascript
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as expected is a good start. Making your programs behave properly when encountering unexpected conditions is where it really gets challenging. ¶ The problematic situations
Javascript Form Error Checking
that a program can encounter fall into two categories: Programmer mistakes and genuine javascript form validation problems. If someone forgets to pass a required argument to a function, that is an example of the first javascript error handling kind of problem. On the other hand, if a program asks the user to enter a name and it gets back an empty string, that is something the programmer can not
Javascript Try Catch
prevent. ¶ In general, one deals with programmer errors by finding and fixing them, and with genuine errors by having the code check for them and perform some suitable action to remedy them (for example, asking for the name again), or at least fail in a well-defined and clean way. ¶ It is important to decide into which of these categories a certain
Javascript Error Trapping
problem falls. For example, consider our old power function:function power(base, exponent) { var result = 1; for (var count = 0; count < exponent; count++) result *= base; return result; } ¶ When some geek tries to call power("Rabbit", 4), that is quite obviously a programmer error, but how about power(9, 0.5)? The function can not handle fractional exponents, but, mathematically speaking, raising a number to the halfth power is perfectly reasonable (Math.pow can handle it). In situations where it is not entirely clear what kind of input a function accepts, it is often a good idea to explicitly state the kind of arguments that are acceptable in a comment. ¶ If a function encounters a problem that it can not solve itself, what should it do? In chapter 4 we wrote the function between:function between(string, start, end) { var startAt = string.indexOf(start) + start.length; var endAt = string.indexOf(end, startAt); return string.slice(startAt, endAt); } ¶ If the given start and end do not occur in the string, indexOf will return -1 and this version of between will return a lot of nonsense: between("Your mother!", "{-", "-}") returns "our
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Web Dev @ Microsoft SEO By WooRank Books Courses Screencasts Newsletters Versioning Shop Forums Advertise Contribute Contact Us Our Story 995kSubscribers 132kFollowers 80kFollowers JavaScript Article A Guide to Proper Error Handling in JavaScript By Camilo Reyes https://www.sitepoint.com/proper-error-handling-javascript/ April 13, 2016 This article was peer reviewed by Tim Severien and Moritz Kröger. Thanks to all of SitePoint's peer reviewers for making SitePoint content the best it can be! Ah, the perils of error handling in JavaScript. If you believe http://www.javascriptlint.com/online_lint.php Murphyʼs law, anything that can go wrong, will go wrong! In this article I would like to explore error handling in JavaScript. I will cover pitfalls and good practices. We'll finish by looking at asynchronous code and Ajax. More from javascript error this author Saved from Callback HellQuick Tip: How to Throttle Scroll EventsGetting Started with the Raspberry Pi GPIO Pins in Node.js I feel JavaScriptʼs event-driven paradigm adds richness to the language. I like to imagine the browser as this event-driven machine, and errors are no different. When an error occurs, an event gets thrown at some point. In theory, one could argue errors are simple events in JavaScript. If this sounds foreign to you, buckle up as you are in javascript error handling for quite a ride. For this article, I will focus only on client-side JavaScript. This write up will build on concepts explained in the article Exceptional Exception Handling in JavaScript. To paraphrase: “with an exception JavaScript checks for exception handling up the call stack.” I recommend reading up on the basics if you are not familiar. My goal is to explore beyond the bare necessities for handling exceptions. The next time you see a nice try...catch block, it will make you think twice. The Demo The demo we'll be using for this article is available on GitHub, and presents a page like this: All buttons detonate a “bomb” when clicked. This bomb simulates an exception that gets thrown as a TypeError. Below is the definition of such a module with unit test. function error() { var foo = {}; return foo.bar(); } To begin, this function declares an empty empty object named foo. Note that bar() does not get a definition anywhere. Let’s verify that this will detonate a bomb with a nice unit test. it('throws a TypeError', function () { should.throws(target, TypeError); }); This unit test is written in Mocha with test assertions in Should.js. Mocha is a test runner while should.js is the assertion library. Feel free to explore these test APIs if you are not already familiar. A test begins with it('description') and ends with a pass / fail in should. The good news is unit te
software. If you encounter any problems, please report them to Matthias Miller at Info