Discuss in detail the impact of lastIndex on regular results

When using regular expressions to check the same string, true and false are returned alternately. In desperation, I looked through the authoritative guide again and found that the culprit turned out to be lastIndex. This article will share with you the impact of lastIndex on regular results.

let reg = /[\d]/g
//undefined
reg.test(1)
//true
reg.test(1)
//false

lastIndex

lastIndex is explained as follows in The Definitive Guide: It is a readable/ written integer. If the matching pattern has the g modifier, this attribute is stored at the beginning of the next index in the entire string. This attribute will be used by exec() and test(). Still using the above example, observe the lastIndex attribute

##

let reg = /[\d]/g  //有修饰符g
//undefined
reg.lastIndex
//0
reg.test(1)   
//true
reg.lastIndex  //匹配一次后，lastIndex改变
//1
reg.test(1)  //从index 1 开始匹配
//false
reg.lastIndex
//0
reg.test(1)
//true
reg.lastIndex
//1

Solution

1. Do not use the g modifier

reg = /[\d]/
///[\d]/
reg.test(1)
//true
reg.test(1)
//true
reg.lastIndex
//0
reg.test(1)
//true
reg.lastIndex

2. Manually set lastIndex = 0 after test()

Detailed explanation of the use of lastIndexOf() method for arrays and strings in JavaScript_Basic knowledge

Usage of indexOf and lastIndexOf Example introduction_javascript skills

js lastIndexOf() usage example

The above is the detailed content of Discuss in detail the impact of lastIndex on regular results. For more information, please follow other related articles on the PHP Chinese website!