Javascript Error Handling Onerror
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Delapouite kscarfone Sheppy Nux SergeG Doekman Rappo GlobalEventHandlers.onerror In This Article Syntaxwindow.onerrorelement.onerrorNotesSpecificationsBrowser compatibilitySee also An event handler for the error event. Error events are fired at various targets for different kinds of errors: When a JavaScript runtime error (including syntax errors) occurs, an error event using interface ErrorEvent is fired at window and window.onerror() is invoked. When a resource (such as window addeventlistener error an or script) fails to load, an error event using interface Event is fired at the element, that initiated the load, and the onerror() handler on the element is invoked. These error events do not bubble up to window, but (at least in Firefox) can be handled with a single capturing window.addEventListener. Installing a global error event handler is useful for automated collection of error reports. Syntax For historical reasons, different arguments are passed to window.onerror and element.onerror handlers. window.onerror window.onerror = function(message, source, lineno, colno, error) { ... } Function parameters: message: error message (string). Available as event (sic!) in HTML onerror="" handler. source: URL of the script where the error was raised (string) lineno: Line number where error was raised (number) colno: Column number for the line where the error occurred (number) error: Error Object (object) When the function returns true, this prevents the firing of the default event handler. element.onerror element.onerror = function(event) { ... } element.onerror accepts a function with a single argument of type Event. Notes When a syntax(?) error occurs in a script, loaded from a diff
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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. ¶ http://eloquentjavascript.net/1st_edition/chapter5.html The problematic situations that a program can encounter fall into two categories: Programmer mistakes and genuine problems. If someone forgets to pass a required argument to a function, that is https://www.tutorialspoint.com/javascript/javascript_error_handling.htm an example of the first kind of problem. On the other hand, if a program asks the user to enter a name and it gets back an empty string, script error that is something the programmer can not 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 javascript error handling important to decide into which of these categories a certain 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, ind
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