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leftContext Property ($`)

Returns the characters from the beginning of a searched string up to the position before the beginning of the last match. Read-only.

RegExp.leftContext

RegExp

Required. The global RegExp object.

The initial value of the leftContext property is an empty string. The value of the leftContext property changes whenever a successful match is made.

NoteNote

The properties of the RegExp object are not available when a program is running in fast mode, the default for JScript. To compile a program that uses these properties from a command prompt, you must turn off the fast option by using /fast-. It is not safe to turn off the fast option in ASP.NET because of threading issues.

The short form for the leftContext property is $`. The expressions RegExp["$`"] and RegExp.leftContext can be used interchangeably.

The following example illustrates the use of the leftContext property:

// Create the regular expression pattern.
var re = new RegExp("d(b+)(d)","ig");
var str = "cdbBdbsbdbdz";

// Perform the search.
var arr = re.exec(str);

// Print the output.
var s = "" 
s += "$1: " + RegExp.$1 + "\n";
s += "$2: " + RegExp.$2 + "\n";
s += "$3: " + RegExp.$3 + "\n";
s += "input: " + RegExp.input + "\n";
s += "lastMatch: " + RegExp.lastMatch + "\n";
s += "leftContext: " + RegExp.leftContext + "\n";
s += "rightContext: " + RegExp.rightContext + "\n"; 
s += "lastParen: " + RegExp.lastParen + "\n";

The output of this program is as follows.

$1: bB
$2: d
$3: 
input: cdbBdbsbdbdz
lastMatch: dbBd
leftContext: c
rightContext: bsbdbdz
lastParen: d

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