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Regular Expressions (English: Regular expression, often abbreviated in code as regex, RegExp, or re) use a single string to describe and match a series of string search patterns that conform to a certain syntactic rule.
Grammar:
/pattern/modifiers;
Pattern (expression, meta-character, quantifier) is represented by patterns. For example: [Abc],[0-9],\d,\s,\b,\uxxxx,n+,n*,n?.
Modifiers is a modifier. I is not sensitive to case, G represents global match; M performs multi-line matching.
Regular expressions are typically used for two string methods: Search () and replace ().
The Search () method retrieves the substring specified in the string, or retrieves a substring that matches the regular expression and returns the starting position of the substring.
The Replace () method is used to replace other characters with some characters in a string, or to replace a substring that matches a regular expression.
The test () method is used to detect whether a string matches a pattern and returns true if the string contains matching text, otherwise false.
The exec () method is used to retrieve the matching of regular expressions in a string. The function returns an array that holds the results of the match. If no match is found, the return value is null.
The TRY statement tests the code block for errors, the catch statement handles the error, and the throw statement creates a custom error.
<! DOCTYPE html>functionmyFunction () {Try{ varX=document.getelementbyid ("Demo"). Value;if(x== "")Throw"Value is empty";if(IsNaN (x))Throw"Not numbers.";if(X>10)Throw"Too Big";if(x<5)Throw"Too small";}Catch(err) {varY=document.getelementbyid ("mess"); y.innerhtml= "Error:" + Err + ". ";}}</script>
It is difficult to write JavaScript programs without Debugging tools. Looking for errors in program code is called Code debugging. Many browsers have built-in debugging tools.
With the debugging tools, we can set breakpoints (where the code stops executing), and you can detect variables as the code executes.
The browser-enabled debugging tool typically presses the F12 key and selects "Console" in the Debug menu.
If your browser supports debugging, you can use the Console.log () method to print JavaScript values on the debug window:
<!DOCTYPE HTML><HTML><Body><H1>My first Web page</H1><P>In the browser (Chrome, IE, Firefox) use F12 to enable debug mode, click the "Console" menu in the Debug window. </P><Script>a= 5; b= 6; c=a+B;console.log (c);</Script></Body></HTML>
In the Debug window, you can set breakpoints for JavaScript code.
The debugger keyword is used to stop executing JavaScript and invoke the Debug function.
JS regular expression, error handling and debugging
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