How to use the exec method of javascript

The exec method of javascript is used to retrieve the match of a regular expression in a string. Its usage syntax is "RegExpObject.exec(string)", and the parameter string represents the string to be retrieved.

The operating environment of this tutorial: windows7 system, javascript version 1.8.5, Dell G3 computer.

JavaScript exec() method

The exec() method is used to retrieve matches of a regular expression in a string.

Syntax

RegExpObject.exec(string)

Parameters

string Required. The string to retrieve.

Return value

Returns an array in which the matching results are stored. If no match is found, the return value is null.

Explanation

The exec() method is very powerful. It is a universal method and is more convenient to use than the test() method and the method of the String object that supports regular expressions. complex.

If exec() finds matching text, it returns an array of results. Otherwise, returns null. The 0th element of this array is the text that matches the regular expression, the 1st element is the text that matches the 1st subexpression of RegExpObject (if any), and the 2nd element is the text that matches the 1st subexpression of RegExpObject The text matched by 2 subexpressions (if any), and so on. In addition to the array elements and length properties, the exec() method returns two properties. The index attribute declares the position of the first character of the matching text. The input attribute stores the retrieved string string. We can see that when the exec() method of the non-global RegExp object is called, the array returned is the same as the array returned by the String.match() method.

However, when RegExpObject is a global regular expression, the behavior of exec() is slightly more complicated. It starts retrieving the string string at the character specified by the RegExpObject's lastIndex property. When exec() finds text that matches an expression, it sets the RegExpObject's lastIndex property to the position next to the last character of the matching text after the match. This means that you can iterate over all matching text in a string by calling the exec() method repeatedly. When exec() no longer finds matching text, it returns null and resets the lastIndex property to 0.

[Recommended learning: js basic tutorial]

Tips and notes

Important: If after completing a pattern match in a string To start retrieving a new string, you must manually reset the lastIndex property to 0.

Tip: Please note that regardless of whether the RegExpObject is global or not, exec() will add the complete details to the array it returns. This is where exec() differs from String.match(), which returns much less information in global mode. So we can say that calling the exec() method repeatedly in a loop is the only way to get complete pattern matching information for the global pattern.

Example

In this example we will globally retrieve W3School in the string:

<script type="text/javascript">
var str = "Visit W3School"; 
var patt = new RegExp("W3School","g");
var result;
while ((result = patt.exec(str)) != null)  {
  document.write(result);
  document.write("<br />");
  document.write(patt.lastIndex);
 }
</script>

Output:

W3School
14

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