Error Handling In Java Script
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Javascript Error Handler
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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 that a program can encounter fall into two categories: javascript catch specific exception Programmer mistakes and genuine problems. If someone forgets to pass a required argument to a
Javascript Try Catch
function, that is an example of the first kind of problem. On the other hand, if a program asks the user to
Javascript Error Object
enter a name and it gets back an empty string, 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 http://www.w3schools.com/js/js_errors.asp 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 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; http://eloquentjavascript.net/1st_edition/chapter5.html 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 mother". ¶ When the program is running, and the function is called like that, the code that called it will get a string value, as it expected, and happily continue doing something with it. But the value is wrong, so whatever it ends up doing with it will also be wrong. And if you are unluc
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