Comparison of the differences between test(), exec() and match() of js regular expressions (with examples)

This article brings you the difference and comparison between test(), exec() and match() of js regular expressions (with examples). It has certain reference value and friends in need You can refer to it, I hope it will be helpful to you.

1. Regular expressions are usually used in

Two string methods: search(), replace()

Two regular expression methods: test(), exec()

search() method: takes a regular expression as a parameter and returns the starting position of the first matching substring, if there is no matching substring , it returns -1.

replace() method: Perform retrieval and replacement operations. Its first parameter is a regular expression, and the second parameter is the string or closure to be replaced.

test() method: Used to detect whether a string matches a certain pattern. If the string contains matching text, it returns true, otherwise it returns false.

exec() method: Used to retrieve matches of regular expressions in a string. This function returns an array containing the matching results. If no match is found, the return value is null.

match() method: The only parameter is the regular expression. Its behavior depends on the flag of this regular expression. If the regular expression contains the flag g, its return value It is an array containing the matches that appear in the string. If the regular expression does not contain the g flag, it also returns an array whose first element is the matched string and the remaining elements are the individual groups in the regular expression. Note: In global search mode, match() does not provide information about the text matched by the subexpression, nor does it declare the position of each matching substring. If you need this globally retrieved information, you can use RegExp.exec().

split() method: is able to support pattern matching.

2. The RegExp object defines two methods for pattern matching, they are exec() and test()

1. RegExp’s exec() method and String’s match() The method is very similar. It performs a regular expression match on a specified string. If no match is found, it returns null, otherwise it returns an array. The first element of this array contains the regular expression. The matched string, and all remaining elements contain the matched groups. Moreover, the index attribute of the regular expression object also contains the position of the string where the match occurred, and the input attribute refers to the retrieved string.
If the regular expression has the g flag, it will set the lastIndex property of the object to the position immediately following the matching string and start retrieval. If exec() does not find any match, it will reset the lastIndex property to 0. This special behavior allows you to call exec() repeatedly to iterate through all regular expression matches in a string.

2. The test() parameter of the RegExp object is a string. If this string contains a match of the regular expression, it returns true, otherwise it returns false
When a regular expression with the g flag When an expression calls the test() method, it behaves the same as exec(), that is, it retrieves the specific string starting at lastIndex, and if it finds a match, it sets lastIndex to the position of the character immediately following that match. , so that we can use the method test() to traverse the string.

test

test Returns Boolean to find whether the pattern exists in the corresponding string.

var str = "1a1b1c";
var reg = new RegExp("1.", "");
alert(reg.test(str)); // true

exec

exec finds and returns the current matching results as an array.

var str = "1a1b1c";
var reg = new RegExp("1.", "");
var arr = reg.exec(str);

If the pattern does not exist, arr is null, otherwise arr is always an array of length 1 whose value is the current match. arr also has three attributes: index is the position of the current match; lastIndex is the end position of the current match (index is the length of the current match); input In the above example, input is str.

The exec method is affected by parameter g. If g is specified, the next time exec is called, the search will start from the last matching lastIndex.

var str = "1a1b1c";
var reg = new RegExp("1.", "");
alert(reg.exec(str)[0]);
alert(reg.exec(str)[0]);

Both of the above outputs are 1a. Now look at the specified parameter g:

var str = "1a1b1c";
var reg = new RegExp("1.", "g");
alert(reg.exec(str)[0]);
alert(reg.exec(str)[0]);

The first output above is 1a, and the second output is 1b.

match

hjvar str = "1a1b1c";
var reg = new RegExp("1.", "");
alert(str.match(reg));

e method is a bit like exec, but: exec is a method of RegExp object; math is a method of String object. There is another difference between the two, which is the interpretation of the e parameter g.

If parameter g is specified, match returns all results at once.

var str = "1a1b1c";
var reg = new RegExp("1.", "g");
alert(str.match(reg));
//alert(str.match(reg)); // 此句同上句的结果是一样的

This result is an array with three elements: 1a, 1b, 1c.

compile method compiles the regular expression into an internal format, thereby executing faster.

var reg = new RegExp();
reg.compile("[a-z]{5}", "g");
alert(reg.test("cftea"));

When using the same regular expression multiple times (such as in a loop), the effect is significant.

Related recommendations:

JS Basic Series Regular Expressions

How to correctly understand the backtracking of regular expressions in js

The above is the detailed content of Comparison of the differences between test(), exec() and match() of js regular expressions (with examples). For more information, please follow other related articles on the PHP Chinese website!