Tip: the pattern "\d" (backslash and lowercase "d") matches a number, and "\D" (uppercase this time) matches any other character. Remember that backslashes must be escaped in strings.
- The first approach is to declare regular expressions using the RegExp constructor. Let's start by using the test() method to check if a pattern is found inside a string variable:
var rgx = new RegExp( "\\d" ); // Create match pattern for a number
var str = "I'm 3 years old.";
if( rgx.test(str) )
alert( "That string contains a number!" );
else
alert( "No number found..." ); - Let's declare another pattern with the constructor, but make it case-insensitive with the "i" flag (or "modifier") as optional second argument - good workaround with limitations of indexOf().
var rgx = new RegExp( "hELlO", "i" ); // mixed-case patternWithout passing the "i" modifier to the constructor, that statement would not have been true!
var str = "I said 'Hello, my name is Charles' to the other guy";
if( rgx.test(str) )
alert( "The word 'hello' appears in that string!" ); - A global modifier "g" lets you find all matches for a pattern - especially useful to "replace()" every single instance. Example: let's remove all non-digits ("\D") from a user-supplied zip code.
var zip = "AhZX77845ASL*$_"; // Zip code between letters and gibberishWithout the global modifier "g", only the first non-number would have been replaced!
var rgx = new RegExp( "\\D", "g" ); // Global: match all non-digits
var clean = zip.replace( rgx, "" ); // Replace all non-numbers with blank
alert( clean ); // returns '77845' - You can use the "regular expression literal" notation, which is shorter and spares you from having to escape simple backslashes: just write "\D" to match a non-digit, no need to write "\\D".
var rgx = /\D/g; // Enclose the pattern between 2 forward slashesLiteral notation is shorter and more legible; modifiers are added right after the second slash.
var zip = "AhZX77845ASL*$_";
var clean = zip.replace( rgx, "" );
alert( clean ); - You can combine modifiers - the regular expression below is both global and case-insensitive:
var rgx = /fox/gi; // Match every word 'fox' and ignore letter casing
var str = "The foxy fox jumps before dancing the Foxtrot";
alert( str.replace( rgx, "wolf" ) ); // Click to run -> - Finally, you can use an anonymous regular expression (no need to declare a variable!)
var zip = "AhZX77845ASL*$_";
// Direct replace pattern with literal notation:
alert( zip.replace( /\D/g, "" ) );
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